Initial stab at inserting tables into table placeholder shapes
Somewhat scruffy spike to "make table shapes from placeholders" work
Oops, make sure to add the nvPr *inside* the nvGraphicFrame when using a table placeholder.
Make sure we're only outputting one nvPr element, as otherwise PowerPoint gets unhappy.
Also re-order the attributes of ph to match PowerPoints
Merge remote-tracking branch 'castaway/feature_insert_table'