Image url preview in MUC conversations

Hi,
I'm just implementing a preview for messages containing just an image url. I have done it only for group chats for now, as there is no other way for sending images yet.
This code is not ready yet, but I just wanted to let others know that I am working on this, and ask for comments.
For example, should there be a preference to switch this on/off, and what should be the default?
Also, is this the right location to place this feature? And there most likely is a better way to look out for images than my very simple regex...
Anyway, I'll continue on this in the next days and let you know.

Yours, Max


![image](https://cloud.githubusercontent.com/assets/388142/4179766/ffc232e2-36d4-11e4-8cb2-74ff2bb86dad.png)