Remove deleted tweets from the channel

[sillygwailo]

This might be possible:

• Twitter sends a 'message deleted' event to the stream if someone from your timeline deletes a tweet.
• Twitter asks client software to honour deletes.
• This will mean having to search messages within a channel and delete messages that only have the tweet URL as the full message. I'll have to use one of the non-real-time Node.js modules for that.