When Master Slide or Master Notes are active,
hides the Common task toolbar as it it not usefull.

Change-Id: Ice07661bf203c029d733614e1eceb5ef3d0661f9
Reviewed-on: https://gerrit.libreoffice.org/16060Reviewed-by: Yousuf Philips <philipz85@hotmail.com>
Tested-by: Yousuf Philips <philipz85@hotmail.com>
(cherry picked from commit 1191ed85)
Reviewed-on: https://gerrit.libreoffice.org/16061Reviewed-by: Jan Holesovsky <kendy@collabora.com>