sw textboxes: reimplement ODF import/export

Turns out that for normal TextFrames and rectangular drawinglayer
shapes, the engine is written in ODF implicitly. Use the same trick to
describe if the shape content should be rendered by SW or editeng.

This reverts 9d310ecfce3c2fc481b125e1493a534e2107a68e (sw textboxes:
implement ODF import/export, 2014-06-02).

Change-Id: Id8afa6368bedcd293e578244abb58e18949bec8d