Volume popup slider doesn't respect current system output device

[fulalas]

Steps to replicate:

1. boot with at least 2 output devices
2. change volume using volume popup slider

Expected behavior: the current system output device should change volume.

Current behavior: the selected device in the drop down (in volume widget settings) changes the volume.

I would either remove this drop down or create a new option to reflect the current system output device because it's very confusing when we change the volume via slider and the actual volume doesn't change.

Also, in pavucontrol to select an output device the tooltip says Set as fallback which isn't very helpful. Something like 'Set as default' would be better, in my opinion.

Doesn't matter the distro or LXQt panel version (including current master from today).