[Enhancement] Extend Synchronize Power option

[Hypfer]

My setup consists of 5 Players A, B C, D are Squeezebox Booms and E is a Transporter which is connected to an amplifier etc.

Most of the time I'm listening on A-D and just sometimes add E. Therefore, I've set the Synchronize Power option of A-D to Power off/on with group.

Now a problem arises when I want to continue listening on A-D but turn off E. Since it's part of the group, turning it off will also turn off the other players. So I have to turn it off, turn the other players back on and then press play again which interrupts the music :(

Therefore, I'm proposing a third Synchronize Power option, which only acts on power events of players inside that group which also have the Synchronize Power option enabled. While I haven't looked at the code, I have a feeling that that should be a simple 3-line addition.

Another approach could be to add something like Power Groups beside Synchronisation groups but that would surely be a much larger change if it's even possible at all. Also, at some point it might make more sense to implement it in an external application since the use-case is just much too specific.