[BUGFIX] Add values to submit buttons

[BUGFIX] Add values to submit buttons

Submit buttons need to have a value set,
otherwise submit checks in the PHP code won't work.

Some useless POST checks are removed after the removal of the
type=image input fields for saving data.

Resolves: #69194
Releases: master
Change-Id: If42da73242d82d96d0042e0bedce69ad2a302427
Reviewed-on: http://review.typo3.org/42764
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Benjamin Kott <info@bk2k.info>
Tested-by: Benjamin Kott <info@bk2k.info>