Add tablet specific landscape layout.

The resolution of the slide preview is too low for a maximised
preview to be of much use, hence it makes sense to make the notes
larger when in landscape mode on a tablet.

Also increase the notes size for tablets (either perspective) in
order to be legible from a greater distance.

Change-Id: Iae75dead6bb325970f2309f487a5c198d938fcb4
Reviewed-on: https://gerrit.libreoffice.org/7102
Reviewed-by: Christian Lohmaier <lohmaier+LibreOffice@googlemail.com>
Tested-by: Christian Lohmaier <lohmaier+LibreOffice@googlemail.com>