This enables FindCommit caching to the following actions:

* BlobController#show
* RefsController#logs_tree

It also improves caching in CommitsController since some
duplicate requests were occuring inside the before_action
definitions.

This reduces a handful of duplicate FindCommit calls while viewing the
projects and commits pages.

Before a 404 would be rendered only after a request to Gitaly would
return with an InvalidArgument error. Now we check that the ref have a
valid format before sending it to Gitaly. In both cases, a 404 is
returned to the user, but this change prevents Gitaly from generating
error noise in production.

Closes https://gitlab.com/gitlab-org/gitaly/issues/1425

This reverts commit 6da19415531e4c40f48df2c604efe51578cea295.

# Conflicts:
#	app/controllers/projects/commits_controller.rb

[master] Resolve "Personal access token with only `read_user` scope can be used to authenticate any web request"

See merge request gitlab/gitlabhq!2583

Enables frozen string for some vestigial files as
well as the following:

* app/controllers/projects/**/*.rb
* app/controllers/sherlock/**/*.rb
* app/controllers/snippets/**/*.rb
* app/controllers/users/**/*.rb

Partially addresses #47424.

This whitelists all existing offenses for the various CodeReuse cops, of
which most are triggered by the CodeReuse/ActiveRecord cop.

When a diff has a significant number of commits, the previous behavior would
attempt to render the Markdown on all the commit messages but only display
1000 of them. To avoid additional work, we only need to render the Markdown
on the set that is displayed.

Since Rails 5.0 `request.format` is being set depending on the route extension.

In commits pages we pass a ref as a URL parameter.
If the ref is an extension-like, Rails converts it and sets to
`request.format`.

E.g. if the ref is `some_branch.atom`, Rails starts responding with
`atom` format, but it should response with `html` because `.atom` is the
part of ref name, not the format.

This commit explicitly sets `request.format` to `:html` when needed.