Add Increase/Decrease font functionality to drawing objects

Change-Id: I9abfca6f8cefd1e1211a98fa36ce07a407c2fd06
Reviewed-on: https://gerrit.libreoffice.org/7655
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>