Rewrote init script.

Rewrite of the GitLab init-script providing the following features:

* Conforms to the Debian, and inherently Ubuntu, init-script guidelines.
  * Is a valid POSIX or /bin/sh script as demanded by the guidelines.
* Keeps track of the Unicorn and Sidekiq and their state separately.
  * Makes sure that both services start and stop appropriately before telling the user that they are or aren't running.
  * Handles cases where one service started and the other didn't. Highlighting it with a red warning text.
  * Knows the running state of both, not just the pids.
  * No longer uses the error prone "ps aux | grep $pid" method for finding out state.
  * Deals with stale pids caused by application crashes.
* User set variables are properly escaped, ensures that paths with spaces in them work.
* No more commands in variables as that sometimes leads to odd edge-cases.
* The script now always runs as the $app_user, not as root or any other user.
* No longer swallows errors produced.
  * This was my initial reason for rewriting the script: GitLab didn't start after an upgrade and there were nothing in the logs and no errors printed by the init script.
* Has passed the peer review of #bash on irc.freenode.org