the initial reason for this change was that graphicsmagick does not
support writing to ico files. this fact lead to a chain of changes:

1. use png instead of ico (browser support is good enough)
2. render the overlays on the client using the canvas API. this way we
   only need to store the original favion and generate the overlay versions
   dynamically.
   this change also enables (next step) to simplify the handling of the
   stock favicons as well, as we don't need to generate all the versions
   upfront.

this ways we can keep the `lib/gitlab/ci/status/*` classes to return the
bare favicon name as it was before.

also the favicon uploader versions are now have the same names as the
stock favicons (+ `favicon_` prefix), which makes working with the
status names easier.

Without the '?' at the end of the favicon url the custom favicon (i.e.
the favicons that are served through `UploadController`) are not shown
in the browser. It may have something to do with how `#send_file` /
`#send_data` set http headers. When serving the same icon file from the
public directory everything is fine.

`#send_file` won't properly set the favicon's content type otherwise.

when versions have a different file format from the original file
carrierwave constructs a wrong url (with the original file suffix).

Pipeline index performance improvements / EE

See merge request gitlab-org/gitlab-ee!5818

Show status information stale icon in Geo admin dashboard

Closes #4909

See merge request gitlab-org/gitlab-ee!5653

 Conflicts:
   app/models/ci/pipeline.rb

Extract EE specific files/lines for app/controllers/groups

Closes #5941

See merge request gitlab-org/gitlab-ee!5947

Fix MR tabs bottom border (EE)

See merge request gitlab-org/gitlab-ee!5982

CE upstream - 2018-06-04 14:04 UTC

Closes #3691

See merge request gitlab-org/gitlab-ee!5962

0af2ab18 decoubled the `to_param`
behavior from `AtomicInternalId`, but this model was forgotten.

Add License Management results in the MR widget

Closes #5487

See merge request gitlab-org/gitlab-ee!5521

Resolve "Geo exposes repository storage paths in HTTP API"

Closes #5380

See merge request gitlab-org/gitlab-ee!5792

# Conflicts:
#   db/schema.rb

Resolve "Merge Request > Security Reports > Vulnerability Modal broken with Bootstrap 4 update"

Closes #6228

See merge request gitlab-org/gitlab-ee!5972

Resolve "Extract EE specific files/lines for some service objects"

Closes #6021

See merge request gitlab-org/gitlab-ee!5796

Exclude Guest users or users without a membership from seats count for Ultimate plan

Closes #5693

See merge request gitlab-org/gitlab-ee!5816

Render a 403 when showing an access denied message

Closes #6259

See merge request gitlab-org/gitlab-ee!5964

Fix Fog mocking (EE)

Closes gitlab-ce#47300

See merge request gitlab-org/gitlab-ee!5977

(EE port) Rephrase Merge Request Maintainer Edit

See merge request gitlab-org/gitlab-ee!5831