Feature: Helper methods for tracking roster and presence

[bklang]

I am writing an IM bot that wants to periodically interact with my online users. Specifically, I want to periodically identify users who are:

• In my roster
• Online
• Available
• NOT already in a specific MUC

...and send them invitations to my MUC. I can request my roster from the server, but it does not contain any presence information. For my application I'll track subscription state internally, but it would be a nice feature if Blather had something built-in that tracked rosters automatically.