Switch & check for playbar TV input

[inopinatus]

I have a playbar and wanted to be able to programmatically switch it to playing the TOSLINK optical input, and to test whether it was currently playing from same. With this change I can do this:

system = Sonos::System.new
playbar = system.find_speaker_by_name('Lounge')
playbar.tv
playbar.is_tv? # => true

and it becomes possible to reverse the Playbar's ungroup-on-autoplay, with an automatic re-grouping when idle:

system.party_mode if system.groups.count > 1 && system.inactive?