Steps of grabFrame
- Init opengl context
- Call libgltf to render
- Get a RGB buffer from libgltf
- Create a Bitmap from this RGB buffer

Additionally:
- Using mimetype is neccessary to decide which player to create.
- bAllowToCreateReplacementGraphic is unneeded.

Change-Id: I7fef043a3341771389144a4f4cac71b0862ef8a7