Proof of concept for XMPP

* Adds an app manifest (we will need systemXHR)
* Adds a working build of node-xmpp-client (browserified)
* Allows to log on (Use a BOSH URL and https) with Jabber
* Allows to send a message to another JID

This is absolutely ugly at the moment, but it's a starting point.
I will now refactor the chat.js into a nice module and prepare the basic UI scaffold to make this a minimal chat application that we can enhance from now on.