Add a global set_up method for the hooks

This method install the post-receive shell script allowing us to have
multiple post-receive hooks per project.
Add the generic post-receive shell script
The hook's install method will require the db object storing the configuration

This in order to set the configuration properly in the git repo and thus
have the hook working.
Start working on the install method of the IRC plugin
Set up the hooks and install them properly (with the right arguments)
Rollback the session if something went south when flushing the session
Add the git_multimail hook from http://git.kernel.org/cgit/git/git.git/tree/contrib/hooks/multimail/
Add a progit Mail hook