[JDEV] Add-on support from Jabber protocol

[Ashvil]

Based on the feedback we got from Thomas Charron on creating some open
extensions to the Jabber protocol, we have a first draft on what we think
would be needed for Magrathea.

We need
a) a way for the client to query what add-ons are installed
b) a way to establish session to the add-on
c) provide the communication envelope between the add-ons.

Here is the proposal in PDF format.
http://dev.i3connect.com/proposal.pdf

I hope we can quickly create a simple wire protocol to support the above
needs. We have tried to design the wire format in accordance with the other
jabber messages but we don't have the long history and expertise in Jabber,
you folks have. So your feedback is highly valued.

Regards,
Ashvil