Support for ZONE2 and ZONE3

[docbobo]

The current extension only supports the Main Zone for Volume Control. It should easily possible to refactor the code so that it also supports ZONE2 and ZONE3. However, things get a little bit more complicated when it comes to also supporting #1.

[docbobo]

Perhaps as user should be able to select the Zones in the settings?

[xkonni]

yes that would be awesome. having 2 rooms connected to my marantz nr1608 as different zones...