Extract ghostclip from ClipElement.
Drag and drop support from the media library.
Hookup the expanders to the timeline stage which now holds the selection
Drag and drop is functionnal once again from the effectslist
Fix mistake in brother ghostclip updating
Re-enables live trimming preview
Add proper licensing to new files.
Rename ClipElement to be synced with GES
We now depend on Clutter 1.12.2
Rehook right click menu items for the layers.

Also make the code a little less stupid.
Allow to insert new layers
Re-enables edition modes
Fix the hiding of handles
Remove roundness of rectangles as Cogl doesn't support antialising.
Update the stage size when dragging objects
 Fix mistake with trim handles
Finalizes layer removal.
Hide the two handles when necessary
Respect low resolution antiquities.
Only generate thumbs when idle