Fixing issue #2970

Mac OS uses launchd instead of /etc/init.d to start daemons and tasks to be started by launchd MUST NOT daemon itself. So "nohup" here won't work for Mac OS. 

Can we add a "launchd" task to the rake file so that we can start sidekiq as "bundle exec rake sidekiq:launchd" ?

A new queue of "project_web_hook" is used to process web hooks asynchronously, allowing each to succeed/fail (and be retried) independently.

(Basically, project web hooks now process the same as system hooks.)

Running the recommendation would give out:
GNU find: paths must precede expression

Fixes #2608

The tasks gitlab:env:info mixes user and group, and presume as a group 'git'.
However, gitolite group name can be anything.

That patch add the git group name in the config,
and check gitolite.ssh_user group against git.group
(which defaults to 'git', as before this patch, if undefined).

M config/gitlab.yml.example:
  Add 'group' in 'git' section
  Mention default value for the two extra settings
M lib/tasks/gitlab/check.rake:
  Check that gitolite.ssh_user *group* is the one defined in git.group.
  Make sure to default to 'git' as the expected group
    if said group is undefined in the config.
  Note: uses a more complete regexp for the group detection
        (the group can start, end or be in the middle or the list of groups
         of gitolite.ssh_user)
M: config/initializers/1_settings.rb:
  Add default values for gitolite.group and gitlab.user

Fixes #2475

Fixes #2496