Blender Git Loki

NLA SoC: Operator for adding new NLA-Tracks

New tracks can be added in the following ways (with the mouse hovering over the channels-list):
* Shift-A - this will add a new track at the top of the stack (i.e. above all the existing NLA-tracks but below the Active Action) for every AnimData block where there was a selected NLA-Track

* Ctrl-Shift-A - this will add a new track above every selected one