This patch adds adjustment layer tracks to the sequencer and does some cleaning
up of the code.
What's an adjustment layer?
Think of it as an effect track, which takes no explicit input, but alters
the output of everything down the layer stack.
So: you can add several stages of color correction with it.
And: you can even use it with metastrips to group several adjustments together.
ui/ --> startup/bl_ui
op/ --> startup/bl_operators
scripts/startup/ is now the only auto-loading script dir which gives some speedup for blender loading too.
~/.blender/2.56/scripts/startup works for auto-loading scripts too.
