Separate PyGST / Gi Gstreamer

This is now easier to understand, maintain, and select. Gi works for python 2.7, and it's the preferred way to get Gstreamer 1.0 working. The previous separation (on PY2) was wrong.

Also, i've managed to correctly read memory data using ctypes with Gi, which is now i do understand what is going on. (instead of relying on gi for reading mapinfo.data, i cast it to a declared structure at the top of the module: `_MapInfo`. This one have the right definition.

@akshayaurora can you have a look ?

refs #1689