[TASK] Base backend login on Twitter Bootstrap

* Change HTML & CSS by using twb
* Cleanup the Controller, e.g remove backend_old setting

Gorgeous brand new login screen for TYPO3 backend.

Resolves: #62180
Releases: master
Change-Id: Idc56f14a22e98d95f49cb73223732f2b17b98fab
Reviewed-on: http://review.typo3.org/33278
Reviewed-by: Felix Kopp <felix-source@phorax.com>
Tested-by: Felix Kopp <felix-source@phorax.com>
Reviewed-by: Ingo Pfennigstorf <i.pfennigstorf@gmail.com>
Tested-by: Ingo Pfennigstorf <i.pfennigstorf@gmail.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Frank Nägler <typo3@naegler.net>
Tested-by: Frank Nägler <typo3@naegler.net>