Some of our users are changing to GitLab as their main repository, it
means that they're disabling the local mirror and setting up a remote
mirror instead. This fix helps to avoid the extra steps required in order
to achieve the desired configuration.

When we update the flag pending_delete to true and later try to 
destroy the remote mirror (through association callbacks) the remote mirror try to load the project, but it is out of the default scope so it just return nil.

As we need the project to remove the reference to the remote mirror but we’re going to delete the project and its repository is not needed to touch the repository to just remove that reference, so we just skip that step in that case

Adds algorithm to the pages domain key and remote mirror credentials encrypted attributes for forward compatibility with attr_encrypted 3.0.0.

aes-256-cbc is the default algorithm for attr_encrypted 1.x, but the default is changed in 3.0 and thus must be declared explicitly.

See https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4216/ for more information. This will prevent OpenSSL errors once the code from that MR is merged into EE.

The `after_save` callback was looking for changes only in the URL without credentials,
this was happening because we store the credentials in a separate field.

* I introduced the new UrlSanitizer class which can help us to protect
credentials used in URLs.
* Renames `.process` class method to `.sanitize`

With this fix we remove the credentials from the repo URLs that are shown when
there is an internal error with Git

* Use Rugged filters to work with local/remote branches.
* Rename Project#remote_mirror? to Project#has_remote_mirror?
* Use delegate pattern for Repository#push_remote_branches and Repository#delete_remote_branches
* Make Repository#remote_tags return Gitlab::Git::Tag objects.
* Refactor Repository#remote_branches
* Rename Repository#push_branches to Repository#push_remote_branches
* Made other small refactors to views and specs.
* Make encrypted_credentials column size bigger.
  This was giving problems with MySql for large passwords.
* Refactor for UpdateRemoteMirrorService spec so we no longer
  harcode the branch names and specs are not broken after `gitlab-test`
  project is updated.

* Also fixed couple of small bugs introduced with last changes

* Also addressed feedback from https://gitlab.com/gitlab-org/gitlab-ee/commit/fcbfe56207f64da07deb7f3a8cbdcd505069edbd

* Now #url= and #url always handle the full URL, encryption is done transparently
* #safe_url was added for future purposes
* Little refactor for UpdateRemoteMirrorService