Twitter Search script

This removes the now defunct twitter_mention.coffee script, given that Twitter [turned off the API today](https://dev.twitter.com/calendar).

Replacing it is a twitter_search.coffee script that uses oAuth against the current 1.1 version of the API. It uses a Bearer token for app-only authentication and also now includes the full tweet text in the room message. 

Also, it incidentally works with the [hipchat](/hipchat/hubot-hipchat) adapter, as the previous script caused an error condition.