In case when the window is to small to show the whole menu then
the use couldn't access the rest of the items in the menu. This
change adds a button in the end (using the ">>" marker as in
toolbar) which on click adds a pop-up that shows the rest of the
menu items.

Change-Id: I9218dba504464bdd44d61ebb383f7674f3df760f
Reviewed-on: https://gerrit.libreoffice.org/46711Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Tomaž Vajngerl <quikee@gmail.com>