Currently the oox import creates a temp file and leaks it, and there is
no way to clean it up afterwards.  Unfortunately it turns out that
SdrModel has no way to access the imported OOXML storage, so add a
really ugly hack to get the embedded media into the SdrMediaObj by
setting both MediaURL and PrivateStream properties (currently oox really
wants to set the properties in alphabetical order too...)

Change-Id: I5a235fbeb08e7bc17faf066de52b94867e9a79a2