The problem was that the shapes produced by the drawingML import had
types like ooxml-triangle, and EnhancedCustomShapeTypeNames::Get() only
handles VML/binary MSO shapes (e.g. isosceles-triangle). Add an OOXML
mode, and in that case use msfilter::util::GETVMLShapeType() instead,
and only fall back to EnhancedCustomShapeTypeNames::Get() if necessary.

Change-Id: Ic93ba4719133dd3e96c17d2562642a03e559fefa