gtkglsink: add "rotate-method" property

Submitted by Olivier Crête @ocrete

Link to original bug (#786991)

Description

This should match the capabilities of glimagesink, this includes support for the AffineTransformationMeta and the image-orientation tag as well as manual rotation using the property.

I didn't do it in glsinkbin becausse the GL happens in the GTK thread in that case.

Version: 1.12.x