... 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: I2d1577bc963d324959b272ed3174571ab197d014
Reviewed-on: https://gerrit.libreoffice.org/51416Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: pranavk <pranavk@collabora.co.uk>