Support multiple common Elgato icon styles

[sebinside]

Currently, there are three common Elgato icon styles for Stream Deck icons that shall be supported:

• Original, i.e., the style the app currently supports
• Modern, a black-white, sharp, minimal style (depends on #110)
• Colorful, with gradients, e.g., seen here

Besides supporting these three styles, we should also find out whether they have proper names by Elgato :) Changing anything beyond the default values should cause a forth "custom" style

[sebinside]

The following options should be possible:

• Elgato Classic (original color scheme)
  • only option: hue
• Elgato Modern (high contrast black and white, FA sharp by default)
  • only option: invert checkbox
• Elgato Neo (Gradient with white symbol), options (might need some internal darkening):
  • Direction (top left / bottom left start)
  • Symbol only checkbox
  • Hue Start
  • Hue Stop (with the option to automatically change with a good default offset)
  • Expert Options:
    • Saturation
    • Translation
    • Lightness
    • Change color space, see: https://gka.github.io/chroma.js/#chroma-mix (default should be lch, see this)
• Custom (RGB selector with hex color code, custom foreground + custom background)
  • RGB foreground (using a nice color picker?)
  • RGB background (using a nice color picker?)