[TASK] Turn todos into @todo to find them easier

Also convert FIXME to @todo.

Change-Id: I98cf8a2c4c732acc7024e36ed949fc4546bee439
Resolves: #63619
Releases: master
Reviewed-on: http://review.typo3.org/35086
Reviewed-by: Markus Klein <klein.t3@reelworx.at>
Tested-by: Markus Klein <klein.t3@reelworx.at>
Reviewed-by: Frank Nägler <typo3@naegler.net>
Tested-by: Frank Nägler <typo3@naegler.net>