Add RBLTableView.

This aims to fix the scrolling craziness that can occur when holding
down arrow keys in NSTableView.

This matches the behaviour of the likes of Mail.app.
Merge from master
Make the RBLTableView header public.
Import the RBLTableView header in the catch-all header.
Merge pull request #80 from github/rbltableview

Add RBLTableView.