After commit 7d66529d7884b73070dbce80b1d4060d841a6933 Add GML3 to
QgsOgcUtils, I have to simplify this class to only have :
* geometryFromGML : read GML2 or GML3
* geometryToGML : create GML2 (as default) or GML3
After the commit 969df016bcdbd1ead8a347b7a5d55c8b36db183a Moved GML import/export to a new class: QgsOgcUtils, I decided to add GML3.
I updated QgsOgcUtils, QGIS WFS Server, and the Python Iterface and I added unit test for GML3.