[TASK] Clean up ext:lowlevel ConfigurationController

Modernize the code base of the lowlevel ConfigurationController:
* No more _GP usages
* Get rid of MOD_SETTINGS and friends
* Don't use BackendUtility::funcModule and other crude helpers
* Get and apply changes to be_user->uc directly
* Move last html pieces to view

Change-Id: I24af6c53b9c55c82e0e1fc1ee79de97768fd9b2c
Resolves: #82754
Releases: master
Reviewed-on: https://review.typo3.org/54389


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Frank Naegler <frank.naegler@typo3.org>
Tested-by: Frank Naegler <frank.naegler@typo3.org>
Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Tested-by: Andreas Fernandez <typo3@scripting-base.de>