Story : automate recovery of gitolite authorized_keys

begin stroy by adding condition to check if the file is empty

Add event in SYSTEM_CHECK

create shell script to automate actions

an email is send if authorized_keys file is empty

increase singleton count

refactor shell script

Provide more feedback

improve bash script

Improve mail content

refactor exception + add new specific exception

move check_authorized now in git_gitolite driver

remove backend dependency

refactor system event

move sh file into git plugin repositories

refactor sh script

Change-Id: I81822b85e1499ee0e93bbfeba2d83979fe9eae18
Merge commit 'refs/changes/85/285/2' of http://gerrit.tuleap.net/tuleap into tuleap-stable-master

* http://gerrit.tuleap.net/tuleap:
  Story : automate recovery of gitolite authorized_keys