[TASK] Finish class alias movings

* Move left over class aliases to ext:compatibility6
* Remove some totally removed alias references
* Add deprecation annotations to LegacyClassesForIde
* Set up LegacyClassesForIde for classes renamed in 7.0
* Add documentation

Change-Id: Ie643d583d7e8663cec89501c6d8c3799fd135cf5
Resolves: #63437
Related: #62013
Releases: master
Reviewed-on: http://review.typo3.org/34793
Reviewed-by: Benjamin Mack <benni@typo3.org>
Tested-by: Benjamin Mack <benni@typo3.org>
Reviewed-by: Mathias Schreiber <mathias.schreiber@wmdb.de>
Tested-by: Mathias Schreiber <mathias.schreiber@wmdb.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>