Better message for failed pushes because of git hooks

Conflicts:
	lib/gitlab/git_access.rb
	spec/lib/gitlab/git_access_spec.rb
Add CRON=1 backup setting for quiet backups
Explain why we create a StringIO
Merge branch 'backup-cron-mode' into 'master'

Backup cron mode

If you have your server configured to receive emails containing the output of
cron jobs it is annoying to get long spammy emails from the backup script. This
change adds a 'cron mode' that makes the backup script silent unless something
goes wrong during the backup.

See merge request !1268
More explicit wording of the documentation.
The release manager handles all releases
Establish ownership of security releases
Bump gitlab-shell
Formatting and sequence of contrubution paragraphs.
Explicitly mention patch releases
Git hook messages: wiki access fix
Merge branch 'master' of github.com:gitlabhq/gitlabhq
Merge branch 'security-release-ownership' into 'master'

Security release ownership

We saw the following problems around the 7.4.4 release:

- the fix got merged into master while it should have been held back
- there was a security fix but no release manager to release it

With this change we want to improve our process and documentation
to prevent situations like this in the future.

See merge request !1273
Merge branch 'git_hook_messages_ce' of dev.gitlab.org:gitlab/gitlabhq

Conflicts:
	GITLAB_SHELL_VERSION
Update time zone rake task for production. Resolves #8387
Merge pull request #8394 from robertd/update-time-zone-in-gitlab-yml

Update time zone rake task for production. Resolves #8387
Selecting a branch is dangerous now that we have rc in a branch.
Change it earlier as well.
Merge branch 'select-a-tag' into 'master'

Select a tag

Related to #1603.

Prevent users looking to install GitLab from source from installing a release candidate by mistake.

See merge request !1274
added office analogy to help understanding of gitlab architecture