no Headphone configured: grey out related controls in skins, open 'Devices' window when clicked

[ronso0]

Any Pfl buttons and Preview deck seem to be ready, even though there's no headphone device configured.
When clicking those controls, no sound would play and there'd be no feedback about why not.

In Tango I greyed out headphone-related controls in case no Headphone is configured, which is (without a tooltip) not much better, but has the advantage of knowing about the situation BEFORE clicking any headphone controls.

Ways to solve this:
A) implement blocking overlays also in other skins:
* add a tooltip and an icon to those blocking overlays.
* provide those overlays a click-action which opens a dialog to either
  set up a headphone device or leave as it is (but know what's going on).

B) keep headphone-related controls how the regularly appear:
* add click-function as Mics have it (1)
* add Cancel button to this dialog

(1) We already have something similar for unconfigured Mic's Talk button, or Vinyl Control toggle or Passthrough toggle (but with out the option to cancel the process), whih could be tuned the same way.

[Daniel Schürmann (daschuer)]

I vote for A
We can it do step by step. The first step in Tango, graying out are nice once you get used to it. We only need to tweak the experiences for first time users.
An additional overlay text "configure headphones" will do the trick.
Please not that we don't have tooltips with touch devices.

[Swiftb0y (swiftb0y)]

Mixxx now uses GitHub for bug tracking. This bug has been migrated to:
https://github.com/mixxxdj/mixxx/issues/9063