Fix: Infinity Bug in Commit Statistics

## What does this MR do?

It fixes a logic bug in the commits statistics: The code assumed that the amount of days involved in a commit range is equal to the difference between the first and last date. This is not true, though, as (from a human standpoint), a commit yesterday and a commit today involve two days, not one. Similarly, a fresh project with only commits made today already 'used' one day.

Since the number of involved days used to be zero for new projects, the result for commits per day quite often amounted to `Infinity`…

## Are there points in the code the reviewer needs to double check?

The test file. I hope it is up to the standards of GitLab.

## Why was this MR needed?

The bug occurres especially for new users with their first project while exploring GitLab.

## What are the relevant issue numbers?

This bug was reported as #1548.

## Screenshots (if relevant)

See merge request !4231

Allow specifying protected branches using wildcards

Closes #18627 

# Tasks

- [ ]  #18627 !4665 Allow specifying protected branches using wildcards
    - [x]  Find existing usages of protected branches
        - Protecting branches
            - `ProtectedBranchesController` is used to mark a branch protected/unprotected
            - `API::Branches` can be used to mark a branch protected/unprotected
        - Enforcing branch protection
            - `Gitlab::GitAccess` has helpers (`can_push_to_branch?`, `check`) that are used to deny pushes if a branch is protected
            - Over SSH: `gitlab-shell` receives a push, and calls `/allowed` on the GitLab API, which calls `GitAccess.check`
            - Over HTTP: 
                - `gitlab-workhorse` receives the request, and forwards it to rails
                - Rails (in the `GitHttpController#git-recieve-pack`) runs basic checks (is the user logged in, not protected branch checks) and returns ok with `GL_ID` and `RepoPath`
                - `gitlab-workhorse` looks at the response, and calls the relevant `gitlab-shell` action from `git-http/handlePostRPC`
                - Rest of this flow is the same as the SSH flow above
    - [x]  Implementation
        - [x]  Backend
            - [x]  Change `project#protected_branch?` to look at wildcard protected branches
            - [x]  Change `project#developers_can_push_to_protected_branch?`
            - [x]  Change `project#open_branches`
            - [x]  Better error message when creating a disallowed branch from the Web UI
        - [x]  Frontend
            - [x]  Protected branches page should allow typing out a wildcard pattern
            - [x]  Add help text explaining the use of wildcards
            - [x]  Show matching branches for each protected branch
                - [x]  ~~On the index page~~
                - [x]  On a show page
                - [x]  Index?
            - [x]  Can't have the "last commit" column for wildcard protected branches
    - [x]  Fix / write tests
    - [x]  What happens if a hook is missing in dev?
    - [x]  Refactor
    - [x]  Test workflows
        - Create a branch matching a wildcard pattern
        - Push to a branch matching a wildcard pattern
        - Force push to a branch matching a wildcard pattern
        - Delete a branch matching a wildcard pattern
        - [x]  Test using Web UI
        - [x]  Test over SSH
        - [x]  Test over HTTP
        - [x]  Test as developer and master
    - [x]  Investigate performance
        - [x]  Test with a large number of protected branches / branches
        - [x]  Paginate list of protected branches
        - [x]  ~~Possibly rewrite `open_branches`~~
    - [x]  Add `iid`s to existing `ProtectedBranch`es
    - [x]  Add documentation
    - [x]  Add CHANGELOG entry
    - [x]  Add screenshots
    - [x]  Make sure [build](https://gitlab.com/gitlab-org/gitlab-ce/commit/2f753e3ed2ce681b4444944d521f4419e8ed37f7/builds) passes
    - [x]  Assign to endboss for review
    - [x]  Address @DouweM's comments
        - [x]  `protected_branch_params`
        - [x]  `exact_match` instead of `explicit_match`
        - [x]  When would self.name be blank?
        - [x]  Move `protected_branches.each` to a partial
        - [x]  Move `matching_branches.each` to a partial
        - [x]  If the branch is in @matching_branches, it's not been removed
        - [x]  move this regex to a method and memoize it
        - [x]  `commit_sha` directly for exact matches
        - [x]  Number of matches for wildcard matches, with a link
    - [x]  Wait for [build](https://gitlab.com/gitlab-org/gitlab-ce/commit/43f9ce0e88194b8f719bb1c1e656b7fc13278d56/builds) to pass
    - [x]  Respond to @DouweM's comments
        - [x]  Don't use iid
        - [x]  Controller should use `@project.protected_branches.new`
        - [x]  move the memoization to `def wildcard_regex`
        - [x]  render with `collection: @protected_branches`
    - [x]  Wait for [build](https://gitlab.com/gitlab-org/gitlab-ce/commit/f7beedf122fa0c7aa89e86181fe7499321fb10ca/builds) to pass
    - [x]  Wait for @DouweM's review
    - [x]  Wait for @jschatz1's review
    - [x]  Respond to @jschatz1's comments
        - [x]  Use the new dropdown style
        - [x]  description should be moved to the description section without the styling
        - [x]  Protect button should be disabled when no branch is selected
    - [x]  Update screenshots
    - [x]  Merge conflicts
    - [x]  Make sure [build](https://gitlab.com/gitlab-org/gitlab-ce/commit/20f3cfe8d5540eab64c2ba548043d600b28c61ba/builds) passes
    - [ ]  Revisit performance, possibly with staging/production data
        - [ ]  Get a dump of staging / run against staging live
            - [ ]  Get SSH access to staging
    - [ ]  Wait for review/merge






# Screenshots

## Creating wildcard protected branches

![1](/uploads/9446afccfdf6fa381e00c800dd2cc82e/1.png)
![2](/uploads/0b154503b297a818d3577488c575d845/2.png)
![3](/uploads/36217f79df9e41cc1550601f02627fe8/3.png)
![4](/uploads/041ca9bd529bcfa5373fca67e917cbcb/4.png)

### Using the `GLDropdown` component

![2016-06-30_14-16-15](/uploads/508afc2a5e2463c2954641409a560d88/2016-06-30_14-16-15.gif)

## Enforcing wildcard protected branches

### From the Web UI

![Screen_Shot_2016-06-20_at_1.21.18_PM](/uploads/8b5d4b1911e9152698a0488daf1880bc/Screen_Shot_2016-06-20_at_1.21.18_PM.png)

### Over SSH

![SSH](/uploads/7365989d7e4c406ef37b6ae5106442c9/SSH.gif)

### Over HTTPS

![HTTPS](/uploads/a7c0f56ae58efcffc75e6700fa2f4ac0/HTTPS.gif)

## Listing matching branches

![Screen_Shot_2016-06-20_at_1.33.44_PM](/uploads/d054113022f5d7ec64c0e57e501ac104/Screen_Shot_2016-06-20_at_1.33.44_PM.png)

See merge request !4665