Adds support for the user interface of Google Apps:

Adds support for the user interface of Google Apps:
* Updates the gapps cron to send out emails on account creation.
* Adds an user page for preferences updates (account creation, account suspension, password change, ...).
* Adds a new mail storage backend, and updates the emails/redirect and emails pages.
* Adds a validation class for Google Apps accounts unsuspension.

Signed-off-by: Vincent Zanotti <vincent.zanotti@polytechnique.org>