Allow LDAP users to change their email if it was not set by the LDAP
server

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/3054

See merge request !2502

Add public params to GET /projects api. Closes #3788



See merge request !2409

# Conflicts:
#	db/schema.rb

This greatly improves the performance of Project#external_issue_tracker
by moving most of the fields queried in Ruby to the database and letting
the database handle all logic. Prior to this change the process of
finding an external issue tracker was along the lines of the following:

1. Load all project services into memory.
2. Reduce the list to only services where "issue_tracker?" returns true
3. Reduce the list from step 2 to service where "default?" returns false
4. Find the first service where "activated?" returns true

This has to two big problems:

1. Loading all services into memory only to reduce the list down to a
   single item later on is a waste of memory (and slow timing wise).
2. Calling Array#select followed by Array#reject followed by Array#find
   allocates extra objects when this really isn't needed.

To work around this the following service fields have been moved to the
database (instead of being hardcoded):

* category
* default

This in turn means we can get the external issue tracker using the
following query:

    SELECT *
    FROM services
    WHERE active IS TRUE
    AND default IS FALSE
    AND category = 'issue_tracker'
    AND project_id = XXX
    LIMIT 1

This coupled with memoizing the result (just as before this commit)
greatly reduces the time it takes for Project#external_issue_tracker to
complete. The exact reduction depends on one's environment, but locally
the execution time is reduced from roughly 230 ms to only 2 ms (= a
reduction of almost 180x).

Fixes gitlab-org/gitlab-ce#10771

Raise hook url limit

1. Up varchar url limit to 2000 chars instead 255
2. Maybe migration?
3. 255 characters - it is not enough
4. nil
5. nil

See merge request !1940

Previously it was "user has already been taken", when really we were
saying the user has already been reported.

Let the CI runner know about builds that this build depends on

This allows us to implement artifacts passing: runner will download artifacts from all prior builds. It will happen automatically, and always, as long as artifacts are enabled.

## The changes:

This MR exposes list of prior builds in CI::API::Builds.

**The API response when asking for builds**

```json
{
  "id": 48584,
  "ref": "0.1.1",
  "tag": true,
  "sha": "d63117656af6ff57d99e50cc270f854691f335ad",
  "status": "success",
  "name": "pages",
  "token": "9dd60b4f1a439d1765357446c1084c",
  "stage": "test",
  "project_id": 479,
  "project_name": "test",
  "commands": "echo commands",
  "repo_url": "http://gitlab-ci-token:token@gitlab.example/group/test.git",
  "before_sha": "0000000000000000000000000000000000000000",
  "allow_git_fetch": false,
  "options": {
    "image": "docker:image",
    "artifacts": {
      "paths": [
        "public"
      ]
    },
    "cache": {
      "paths": [
        "vendor"
      ]
    }
  },
  "timeout": 3600,
  "variables": [
    {
      "key": "CI_BUILD_TAG",
      "value": "0.1.1",
      "public": true
    }
  ],
  "dependencies": {
    "builds": [
      {
        "id": 48584,
        "ref": "0.1.1",
        "tag": true,
        "sha": "d63117656af6ff57d99e50cc270f854691f335ad",
        "status": "success",
        "name": "build",
        "token": "9dd60b4f1a439d1765357446c1084c",
        "stage": "build",
        "project_id": 479,
        "project_name": "test",
        "artifacts_file": {
          "filename": "artifacts.zip",
          "size": 0
        }
      }
    ]
  }
}
```

## How it will work?

**Example:**
```
build:
  type: build
  script:
  - echo TEST > test_file
  artifacts:
    untracked: true

rspec:
  type: test
  script:
  - test-my-project

staging:
  type: deploy
  script:
  - scp test_file root@server.com:
```

**The flow:**
1. We run `build`. The `build` creates a file `test_file`. This file gets archived and send us build artifacts.
2. We run `rspec`. The `rspec` downloads build artifacts from `build`. Uses the `test_file`.
3. We run `staging`. The `staging` downloads build artifacts from `build` and `rspec`, but since the `rspec` doesn't have build artifacts we skip that build. Deploys the `test_file`.

This partially implements the https://gitlab.com/gitlab-org/gitlab-ce/issues/3423.

In the next release we will introduce option to configure what artifacts are received.

/cc @grzesiek @DouweM @sytse @rspeicher


See merge request !2437