This should significantly simplify these panels, by not forcing
them to override GObject.constructed all the time. Most panels
were quite straightfoward.
This commit changes the switch to do a proper delayed state change using
the state-set signal. Also changed is that we always update the switch
state rather than avoiding an update when it is not powered.
Avoiding this update was introduced in commit 4a009da483 (bluetooth:
Don't change the switch status when transitioning), however, the current
implementation causes us to get stuck in the wrong visual state
sometimes. Also, with this patch I am unable to see any visual glitch on
hardware that should be affected, and even if there was a glitch,
getting the final state right is more important.
Closes: #607, #1272
