Make layer.screenFrame a property

You can now directly get/set the screenFrame for each layer (layer.screenFrame used to be a function). I also got rid of the Frame object in many places in favor of a normal object.
Undo accidental addition
Add experimental OmitNew

So you can omit the new keyword for *Layer, Frame and Animation.
Merge remote-tracking branch 'upstream/master'
Add a global time scale for slowing down animations for fine tuning