This is the first step to integrates some Git repositories housekkeping scripts in Tuleap;

This feature aims to:

1-We'll add a simple cron job that walks thru the list of repositories in a given timeframe (two params, runtime_start and runtime_end, to be given to the cronjob), and chatch repositories that needs to be garbage-colelcted (we do not implement the GC in this change).

2- Repositories caught by the check are added to a dedicated housekeeping table witihn DB, we keep also a trace in git_syslog.

3- A fourth pane is added to the git plugin interface within site admin where we display all git repositories flagged as "bad".