bin: Use fetch instead of remote update
pitivi: Port to the new commit based API in GES
project/timeline: Port to new Track API
Add a show keyframes button which calls a show Keyframes method on the relevant timeline element
This commit makes addition of keyframes possible.

Conflicts:
	pitivi/timeline/elements.py
	pitivi/timeline/timeline.py
Usability work.
timeline/elements: keyframe refactoring.

	+ Moves the keyframe code from URISourceElement to TimelineElement.
timeline/elements: Edge keyframes can't have their timestamps changed.
timeline/elements: clamp timestamps and values.
timeline/{elements:timeline} : Unselect keyframes on dragEnd if needed.

	+ Get the pointer device in timeline.
	+ Check if it is on the keyframe at drag_end in elements.
timeline/elements: add a way to remove keyframes.

It's possible to remove keyframes now by holding CTRL and clicking a keyframe.
timeline/elements: hide keyframes when the element is not selected.
utils/pipeline: seekRelative(0) is a legitimate case.