This partially reverts 6a5cd3ca - we keep the migration and add a new
migration that reverts it in order to keep migration history intact.

Introduced by me through !2005

InfluxDB over UDP doesn't use authentication, thus there's no need for
these settings.

[ci skip]

This removes the need for Sidekiq and any overhead/problems introduced
by TCP. There are a few things to take into account:

1. When writing data to InfluxDB you may still get an error if the
   server becomes unavailable during the write. Because of this we're
   catching all exceptions and just ignore them (for now).
2. Writing via UDP apparently requires the timestamp to be in
   nanoseconds. Without this data either isn't written properly.
3. Due to the restrictions on UDP buffer sizes we're writing metrics one
   by one, instead of writing all of them at once.

- Offloads uploading to GitLab Workhorse
- Use /authorize request for fast uploading
- Added backup recipes for artifacts
- Support download acceleration using X-Sendfile

This option only existed to ease the CI-to-CE/EE migration process.

This commit partially reverts 8b05abe8

Fixes #2536
Signed-off-by: NJeroen van Baarsen <jeroenvanbaarsen@gmail.com>

delay is in seconds
more legible code in session_store
Added `GitLab restart required` help block to session_expire_delay

settings

This feature was requested long ago:

http://feedback.gitlab.com/forums/176466-general/suggestions/4118466-ability-to-register-only-from-ceratain-domains

This MR is based off !253 but changed to use application settings and use wildcard strings
to give more flexibility in pattern matching. Regexps seemed overkill and easy to get wrong.

Only restrict e-mail addresses upon creation

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

Add new global application settings for default project and snippet
visibility levels.

Fix bug where error messages from Dropzone would not be displayed on the issues page

Closes #1258