+ added icon to the notebookbar, after click the file menu will appear

Change-Id: I30e1ed7e2c4a194e150c7196652904fd4e5c9e8e
Reviewed-on: https://gerrit.libreoffice.org/27347Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Samuel Mehrbrodt <Samuel.Mehrbrodt@cib.de>