Remove Rebel.framework and import just RBL(Clip/Scroll)View

- Resolves compiling on OSX10.10 SDK
  - Rebel wasn't maintained anyway
- RBLTableView didn't do anything anyway, so we can just use NSTableView
- RBLScrollView was forcing layer backing and speeding it up
  - See http://jwilling.com/optimized-scrolling-in-nstableview for more
    info
- Just directly import RBLClipView and RBLScrollView into our repo
- Had to modify the backgroundColor methods of RBLClipView, as they used
  helper functions defined in Rebel.framework
  - These may not be the same as the Rebel.framework ones did something
    a lot more complicated
  - AFAIK we don't use them anyway though
- Updated LICENSE to include Github copyright

- Closes #48