Rearranged activity_main.xml in order to fix the bug
of app bar invisible on lower versions of Android
devices.

Change-Id: Ic4ec9435ce9ef55a2596600c143114c899c30ac2
Reviewed-on: https://gerrit.libreoffice.org/36950Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Tomaž Vajngerl <quikee@gmail.com>