New API to suspend/activate users

Admins have now two new APIs:
PUT 	/admin/user/suspend/:username	
PUT 	/admin/user/activate/:username	

The first suspend a user (neither delete him nor his contents), the second one reactivate it.
When a user is suspended, he/she cannot login or perform any API call.

Users can suspend themselves using the API:
PUT 	/user/suspend

At this moment, only Admins can reactivate auto-suspended users.