*BackGraphicURL include the following properties:
- BackGraphicURL
- FooterBackGraphicURL
- HeaderBackGraphicURL
- ParaBackGraphicURL

This were removed, but for backwards compatibility this commit
adds them back again and depreactes them in the UNO API. The
behaviour also changes as internal vnd.sun.star.GraphicObject
scheme URLs aren't supported so this properties can only be set
and only if a external URL is provided. If getting such a property
then a RuntimeException will be thrown.

[ Miklos Vajna: fixed up sw/qa and writerfilter bits. ]

Change-Id: If60011837da96197b576bfe2671ecafccad736c7
Reviewed-on: https://gerrit.libreoffice.org/53511Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Tomaž Vajngerl <quikee@gmail.com>