FillBitmapURL was restored so when setting the property, it loads
the Bitmap from the provided URL and creates a XBitmap. Get is
not supported anymore however.

Change-Id: Ie250d9f751ba33fc45b759dd3a773b4ec5c864d3
Reviewed-on: https://gerrit.libreoffice.org/53443Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Tomaž Vajngerl <quikee@gmail.com>