[TASK] Remove dependency on EXT:cshmanual

Adding some preliminary isLoaded functions
in order to allow to uninstall EXT:cshmanual
and thus, be able to hide the full toolbar item.

The long-term solution should still be to
implement a new help concept and drop
cshmanual, the csh icon and TCA_DESCR

Releases: master
Resolves: #63146
Change-Id: I45a27ea03c75527b331fc10951047ee10fb05e28
Reviewed-on: http://review.typo3.org/34243
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>