show ControlPotmeter and EffectParameter values in skins

[Be]

We describe the scales of effect parameters in parameter tooltips, but it is impossible to know exactly what value a knob is at. It would be really helpful to show this beside the knob. I think Traktor does this quite well. In Traktor, the value of a knob replaces its label while the knob is being adjusted. Watch this video for an example: https://www.youtube.com/watch?v=rRg0fXlYYDI&t=4m40s

Related: Bug #1419949

[Be (be.ing)]

For effect parameters, we should create a way for effects to specify human readable formats of their values, for example dB, percentage, or beat fraction.

[ronso0 (ronso0)]

This would be extremely helpful for sync'ed paramters like Echo's Time.
Until now I didn't dare to touch these knobs when Sync is On because it's lacking the feedback when snapping to a value.

[Be (be.ing)]

Pushing this to 2.3.0 so I can focus on the library redesign branch.

[ronso0 (ronso0)]

The way Traktor does it is really elegant. I guess this works well for mouse and controller usage, but we should also consider touch screens where fingers might cover the parameter name.
We could show the value in a small popup, using the tooltip mechanisms for placing it appropriately (left or right).

[Swiftb0y (swiftb0y)]

Mixxx now uses GitHub for bug tracking. This bug has been migrated to:
https://github.com/mixxxdj/mixxx/issues/9022