track: adds set_mixing and get_mixing.
timeline-pipeline: make caps writable in SMART_RENDER.
Test-utils: Add test file generation code.
tests: Add rendering tests.
Rendering tests: WIP
tests:render: Add MOV tests, as they are a classic camera format (canon 5D)
Rename render to integration.

	+ This is the real scope of that branch
	+ Adds a check-integration rule.
tests/integration: do playback and render tests.
integration tests: add a forever test.
tests/integration: port to commit based API.

	+ Only set_render_settings on the pipeline when necessary.
tests/integration: add the stem of a (already failing) new test.
framepositionner: fix messup with propname enum.
track-element: No need to log when prio == MIN_GNL_PRIO.
integration: add the stem of an image test.
integration: adds a video layer to the image test, playback doesn't start.