feat: add file and color controller setting types

[acolombier]

Add new controller setting type, particularly useful for screen mapping.

Screencast.from.19-09-24.10.02.23.mp4

TODO:

• Unit test
• Improved UI

[JoergAtGithub]

These setting types are great features!

For the file selector I would expect a widget like this:

and a XML settings for the allowed file types.

More complicated might be a generic definiton for colors, as:

• we have already certain purpose specific colormaps:
  
• but more important here, many controllers have only a small list of supported colors, as this list of named colors:

  mixxx/res/controllers/Traktor-Kontrol-S3-hid-scripts.js

  Lines 149 to 171 in 067792b

  	// The S3 has a set of predefined colors for many buttons. They are not
  	// mapped by RGB, but 16 colors, each with 4 levels of brightness, plus
  	// white.
  	this.hid.LEDColors = {
  	OFF: 0x00,
  	RED: 0x04,
  	CARROT: 0x08,
  	ORANGE: 0x0C,
  	HONEY: 0x10,
  	YELLOW: 0x14,
  	LIME: 0x18,
  	GREEN: 0x1C,
  	AQUA: 0x20,
  	CELESTE: 0x24,
  	SKY: 0x28,
  	BLUE: 0x2C,
  	PURPLE: 0x30,
  	FUCHSIA: 0x34,
  	MAGENTA: 0x38,
  	AZALEA: 0x3C,
  	SALMON: 0x40,
  	WHITE: 0x44
  	};

• our current color mapper API has no link to the XML yet: https://github.com/mixxxdj/mixxx/blob/main/res/controllers/color-mapper-api.d.ts
• Maybe we need a solution to define a color map from XML instead of JavaScript?

[acolombier]

Thanks for the early feedback!

For the file selector I would expect a widget like this:

Yes, that makes sense. It's in the todo list already :)

we have already certain purpose specific colormaps:

The current widget are more tailored for palette AFAIK, not unique colour selection, so not sure how to do this? I was thinking of adding a color indication inside/next to the pick button

but more important here, many controllers have only a small list of supported colors, as this list of named colors:

Yes, this usecase is already covered with enum, and actually used by the S4Mk3. One bits of improvement could be to add some color indication in the dropdown, I guess we could easily add an attribute on the option element if we wanted to improve the UX for those?

[Swiftb0y]

I think using the Qt color picker is fine. If we want to we can pre-fill their color with for example the users currently track-color palette (the palette source could also be configured as part of the setting). But lets KISS for now until we have a good reason to couple this to our palettes. A palette selector could be interesting indeed, but that is separate from the color picker.