Add support for AWS S3 Server-Side Encryption support

This adds support for AWS S3 SSE with S3 managed keys, this means the
data is encrypted at rest and the encryption is handled transparently to
the end user as well as in the AWS Console.

## Points to double check
I'm unsure on the best way to the handle the default. I've followed the `multipart_upload` de facto in the app. I'm happy to change this if required or if it will impact elsewhere e.g. omnibus packages

I also think I've managed to catch all of the documentation for this change as well.

### Why is this required
Many enterprises require good backup support but also for this to be encrypted. By default backups aren't encrypted, this allows at rest encryption to be supported in GitLab backups providing a layer of security should the physical media not be properly disposed of.

Relates to issue #2478.


See merge request !1280

Documentation of omniauth-ldap limitations

Further documentation about limitations directly impacting settings of
users' LDAP servers.

Closes #2613

See merge request !1421

Improve repo cleanup task

I accidentally wrote a new script, not seeing we already had one.
But the old one did not do enough (it only handled global namespace orhpans) so I figured I should just drop in the new script.

See merge request !1298

page-title-fix

Fixed .page-title margin

See merge request !1458

Move CI variables page to project settings
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Part of #2594 

See merge request !1457

Remove 'kerberos' from auth_helper.rb for gitlab-CE.

There is no Kerberos auth in gitlab-ce, so it shouldn't be noted
as a form-driven auth mechanism in app/helpers/auth_helper.rb.
This breaks using Kerberos as a custom omniauth provider.
See issue #2510 (https://gitlab.com/gitlab-org/gitlab-ce/issues/2510).

@DouweM suggested I send in this merge request.

See merge request !1430

note about EE git hooks

Because of https://gitlab.com/gitlab-com/www-gitlab-com/issues/415#note_2131220

See merge request !1934

[ci skip]

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Update Source Sans Pro font: adds support for cyrillic characters
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Fixes #2764

See merge request !1454

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Add user preference to view project activity and starred project activity as default dashboard

Screenshot:

![image](https://gitlab.com/gitlab-org/gitlab-ce/uploads/5e39fa66da50e01dd9ed1c8a9ce01ea9/image.png)

Closes #2662

See merge request !1446

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Fix grammar in admin area labels when no labels exist

Fixed grammar on Using Docker Build doc.



See merge request !1448

updating admin area > "Labels" text to "There are no labels yet.", per Stan Hus suggestion.

Closes #2662

FogBugz Import: Include closed comments since they may contain user data

Correct an inaccuracy in the Markdown doc

[ci skip]

See merge request !1445

[ci skip]

refactoring buttons, fixes for projects filter on the dashboard and
group page

Add unreleased 8.0.3 entry to CHANGELOG

[ci skip]

See merge request !1440

[ci skip]

[ci skip]

This adds support for AWS S3 SSE with S3 managed keys, this means the
data is encrypted at rest and the encryption is handled transparently to
the end user as well as in the AWS Console. This is optional and not
required to make S3 uploads work.

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>