Global Presence

[David Edmundson]

All the above plan doesn't work:

The problem:
 - We always (on advice from Empathy guys too) show the global
presence as the "highest presence of all accounts". However this
breaks using extended-away with local XMPP enabled.
If we select extended away, local-xmpp (in MC) falls back to simply
"away". Away is higher than anything extended away so your global
presence now shows up as "away".
This is makes for a very confusing UI where it appears to select
something different to what you pressed, not cool.

Empathy gets round this by only showing "Available, Busy, Away,
Invisible, Offline".

I've no idea how we should solve this, short of ugly hacks.