Put properties in their own structure

The structure will be the entry point for static variables in latter patches

Change-Id: Iaa072591b1c900598c4f8ebf386e9b51342967dd
Reviewed-on: https://gerrit.libreoffice.org/12477
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>