[BUGFIX] Repair overrideVals for FormEngine

While passing values via GET or POST, those values have been lost
to the form. The handling has passed to a dedicated element class,
that handles them correctly.

Change-Id: If41ae361e8e4fd4012a13bf888dc62d94d5e079c
Resolves: #69784
Resolves: #69661
Resolves: #69664
Releases: master
Reviewed-on: http://review.typo3.org/43304


Reviewed-by: Susanne Moog <typo3@susannemoog.de>
Tested-by: Susanne Moog <typo3@susannemoog.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>