PPTX import: shape effect properties defined by theme

Effect import is so poor by now that this changes does not seem
to have any effect, but later it can be helpful.

See also:
81cd386facedfbb15be6dffc10351262abf733f3
and
664a56b3c81503bdf199edf1806676f0a35b956f

Change-Id: I4e6a9952aa138959ab273db0494ef0cf76d8fc24