In the tabbed notebookbar the shortcuts toolbox is introduced.
It is placed before tab labels, after the menu button.
Customization is possible, buttons are loaded from the
newly created toolbar "Notebookbar shortcuts".

NotebookbarTabControl was moved to the sfx module.

Change-Id: Ifa4a1688c6e92c2f03bd386608e3e9d1c28069d4
Reviewed-on: https://gerrit.libreoffice.org/35194Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Samuel Mehrbrodt <Samuel.Mehrbrodt@cib.de>