The new system extension form needs some changes:

* move global variable and initialization to tx_form_Common
* rename class name of form controller to reflect directory hierarchy
* move PageTSconfig and TypoScript configuration to Resources/Private/
* remove superfluous configurations and definitions

Change-Id: Iec38b53099edcb170c6d8b802e73b381602ff27d
Resolves: #28655
Reviewed-on: http://review.typo3.org/3998
Reviewed-by: Oliver Hader
Tested-by: Oliver Hader