Add followPermalink shortcut

I implemented a new keyboard shortcut to open the current comment's permalink. Default key is currently 'Y' for opening in current tab, 'shift-Y' for opening in new tab. I chose that because it isn't currently assigned to anything else, so feel free to change it.

http://www.reddit.com/r/Enhancement/comments/20qlmj/feature_request_keyboard_shortcut_to_open/