[TASK] Simplify rendering in EXT:scheduler

Don't use the DocumentTemplate class to render a simple table.

Changes are:
 * Simplify the rendering of the available classes
 * Change existing form to a proper markup using forms instead of tables.

Resolves: #62330
Releases: master
Change-Id: Id7d37e323dea1ce4e0dad7ef61efafaa04ac960f
Reviewed-on: http://review.typo3.org/33394
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Benjamin Mack <benni@typo3.org>
Tested-by: Benjamin Mack <benni@typo3.org>