Refactor gitolite repository configuration serialization

Behaviour change: instead of amending an existing file and adding tuleap stuff
this commit will write the whole file based on defined template.

However, to let site admin tweak their gitolite main config (I pretty sure
gitweb needs it) we support an override mecanism.

To active it, you should copy
/usr/share/tuleap/plugins/git/templates/gitolite/gitolite.conf.mustache
into
/etc/tuleap/plugins/git/templates/gitolite/gitolite.conf.mustache
and add your own config

Change-Id: I0a2a577ab6e41dae5161dfc1b4904d877ffabce3
Merge commit 'refs/changes/09/3109/5' of ssh://gerrit.tuleap.net:29418/tuleap into HEAD

* ssh://gerrit.tuleap.net:29418/tuleap:
  Refactor gitolite repository configuration serialization

Change-Id: If64c7401bb2a0cf43e4e6fda1ffb60b6641acc7f
This is Tuleap 7.5.99.61

Change-Id: I3fffda94a43f3a59a30b15c7000c8ac1f023ba67