Community addons

Some changes to runbot in order to better test with community addons

When testing a repo which does not contain odoo, but addons from OCA:
* Only test modules from the repo, don't test all of odoo's addons
** opener-hr will only test hr-related addons
* Test Community addons in openerp/addons-to-test instead of openerp/addons to better separate them from official addons
* Add dependency repos field to specify additional addons to fetch
** Some OCA repos depend on modules found in other OCA repos
** These are installed in openerp/openerp/addons-extra-dependencies to better separate them and to avoid testing them which could result in an un-ending chain of repo dependency
* Add function which will find the most likely main branch a PR comes from
** using the git merge-base and git log commands
Indeed I do. This can be done, we just have to be careful to separate odoo repos and module repos.

I meant it was more intrusive, changing the tables (many2one -> many2many) as well as the column name.
This might require a bump in the version and a migration script.