As we want to get rid of GraphicObject URLs for the more robust
image life-cycle handling, it was necessary to change the way
bitmap table stores and handles images, so that they always
store a Graphic object (wrapped in UNO object that provides the
XGraphic and XBitmap interface).

In addition this changes loading and saving from ODF (xmloff) and
OOXML (oox) filters so they don't depend on GraphicObject URL
anymore, but load or save directly to / from  XGraphic or XBitmap.

Change-Id: I2b88e10056e7d6c920249d59188f86b1a5a32d21
Reviewed-on: https://gerrit.libreoffice.org/49074Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Tomaž Vajngerl <quikee@gmail.com>