Rearranging layers with hotkeys

[Keavon]

Ctrl[ lowers the selected layer(s) in the stack, Ctrl] raises, and the Shift modifier raises the selected layer(s) all the way to the top or bottom. Raising and lowering is constrained to the folder for now. Leave a // TODO for handling the case where layers from multiple separate folders or depths in the folder hierarchy are selected when trying to raise/lower.

[ajweeks]

I'm going to take a stab at this one 🙂