Autolink chat and forums

I've used the Autolinker.js project (https://github.com/gregjacobs/Autolinker.js) to add automatic linking of emails, URLs, and twitter handles.

Chat messages and forum posts will be automatically linked (should work for old posts too).

I've found a bug when URLs are surrounded in quote marks, but that is to do with Autolinker and I think is a small problem! Hopefully we can address that up-stream and then it will be fixed for us too.

Implements #48