Move pair keybindings out of default to a behavior

This addresses pair keys clobbering non-pair keys for 8-12 keyboard layouts as [explained here](https://github.com/LightTable/LightTable/issues/620#issuecomment-59621776). This is a change that will require users who want pair keybindings to bring in the new behavior. I didn't bring in the single quote keybinding since we may revert 82fe8cbfc8001c550182b8ae900c022d003e46c5.
@ibdknox I looked in node-webkit issues and didn't see many keybinding issues so I don't see how this would be fixed there. Since we use mousetrap for keyboard layouts, it's possible this could eventually be fixed by them. I do see open issues for keyboard layouts there e.g. ccampbell/mousetrap#143 and ccampbell/mousetrap#191