This ensures the caches for Repository#empty? and
Repository#has_visible_content? are flushed after a repository has been
imported or forked.

Fixes gitlab-org/gitlab-ce#13505

The "default_branch" argument is never used and the "project" argument
isn't optional.

Since gitlab_git 8.0, blob data are lazy-loaded so we have to call
blob.load_all_data!(repo) to eager-load them.

Fixes #13458.

Prior, if the request format was, for example, .zip, we'd get an
`ActionView::MissingTemplate` error.

Closes #13467

1. We now display the index of the current issuable among all its project's
issuables, of the same type and with the same state.
2. Also, refactored a bit the Issuable helpers into a new IssuablesHelper
module.
3. Added acceptance specs for the sidebar counter.

Steps to reproduce:

1. Go to a MR or issue
2. Click on "thumbsup" Emoji 3 times
3. Observe the tooltip becomes "me, me"

Closes #13374, #12788

- Apply the RelativeLinkFilter filter to other formats, e.g.,
  reStructuredText so links from the Files view or the Project view work
- Remove the AsciidocPipeline pipeline

Fixes #3533.

Closes #13199

- Add `avatar_url`, `description`, `git_ssh_url`, `git_http_url`,
  `path_with_namespace` and `default_branch` in `project` in push, issue,
  merge-request and note webhooks data
- Deprecate the `ssh_url` in favor of `git_ssh_url` and `http_url` in
  favor of `git_http_url` in `project` for push, issue, merge-request and
  note webhooks data
- Deprecate the `repository` key in push, issue, merge-request and
  note webhooks data, use `project` instead

Prior, it would only be shown if the issue had been edited.

We keep this only for backwards compatibility with projects that have
been migrated from GitLab CI. New project badge will go elsewhere.

In case merge request is broken, we shouldn't check if the sha
is mergable, as it will be null, and there's no point, as we know
that it's not mergable.

Closes #13254

Also:
- Get rid of legacy :strict_mode
- Get rid of custom :email validator
- Add some shared examples to spec emails validation

Instead of flushing the behind/ahead counts for all branches upon every
push we now only flush the cache of branches that actually need to have
these statistics recalculated. There are now basically 2 scenarios and
their effects:

1. A user pushes a commit to the default branch, this results in the
   cache being flushed for all branches.
2. A user pushes to a non default branch, this results in _only_ the
   cache for that branch being flushed.

The existing code (Repository#expire_cache) remains backwards compatible
with the previous behaviour, the new behaviour is only applied when a
branch name is passed as an argument. This ensures that when for example
a project is deleted the cache for all branches is flushed.