Add periodic session checking/updating

[ho0ber]

While we can do smarter hooks eventually, the simpler approach for now is to periodically poll device volume channels.

The simple approach here is:

1. Get a handle on the master device volume session to hold on to
2. then, every X seconds, poll for all application volume sessions and just fire the raw data down the pipe
3. In the event handler, compare active sessions to channel's target's sessions and set or unset a "dead" flag on channels to show if their sessions are dead?

[ho0ber]

fe82061