... such that during insertion of objects when sd calculates the center
of the view to place the object, it is the center of the whole slide,
not the center of the default rectangle of 800x600.

It's also important to hide rulers, scrollbars so that correct center is
calculated; we don't need them anyways in LOK.

Change-Id: I1180541c1b8c8a35f39112ca0a670c9d96d1320b
Reviewed-on: https://gerrit.libreoffice.org/51357Reviewed-by: Jan Holesovsky <kendy@collabora.com>
Tested-by: Jan Holesovsky <kendy@collabora.com>