ges-source: Move sub element handling to the base class.

	    + And port all the subclasses.
utils: Adds the create bin method there to be used internally.
test sources: Modifies the way we handle properties such as pattern.

     + This makes make check pass.
     + This standardizes property handling.
sources: Starts adding video-uri-source et al. WIP fix up on me.
Removes old uri-source
Documentation updates.
GES: Implement audio and video source.
GES: Port all sources to inheriting from audio / video base sources.

That was painful.
videotransition: No need to hard set width and height anymore.
ges-track: Remove the set_caps from the API, keep it internally.

    + Add restriction caps instead.
    + gnonlin sets these caps on all its children, which
	     is not really convenient.
gstframepositionner: Install width and height properties.

    + And manage them properly.
test-utils: Adds a utility function to quicly check the timeline.

    + It takes a dump_to_dot argument as a free bonus.
timelineedition test: Adds a test_scaling.

    + It will check that the clip updates its size correctly.
    + Will certainly move elsewhere.