It now lists all command categories which can be
added based on the current module (writer, calc etc.)

This class will be expanded later with macros and styles
handling stuff. It will also update the commands listbox
when it is added.

Change-Id: I4f50408641db067118f63fe0e9a1ee755873412f
Reviewed-on: https://gerrit.libreoffice.org/40833Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Katarina Behrens <Katarina.Behrens@cib.de>