gulafaran's and vodik's improvements.

[vodik]

This is a fresh implementation of @gulafaran's feature set over master. Should be cleaner and better organized. I did not port his per-application support since a much better implementation could be done (it only exposes sinks, no sources).

Major changes:

• Support for enumerating and controlling both sinks and sources
• Add defaults command and set that to be the default command (instead of list)
• Add set-balance and get-balance actions
• Rename set-sink to set-default and make it support both sinks and sources
• Add is-muted command

[vodik]

I have per-application stuff done in a proof of concept stage, I'll make a separate pull request for it when its ready.

[falconindy]

Awesome, I've merged everything except 3ae335d -- the name makes sense because it applies to what its used by, not what it retrieves.