Upgrade Bootstrap to 3.0.0

Bootstrap 3.0.0 has been released on 19th of August and we should consider upgrading. 2.3.2 is not actively maintained anymore and we are still on 2.3.1.

__Edit__: by now 3.0.1 has been applied.
__Edit 2__: by now 3.0.2 has been applied.
__Edit 3__: by now 3.0.3 has been applied.