Color Picker Improvements

[Holzhaus]

• Switch to QFlags for color picker options
• Minor code cleanup
• Add support for picking custom, non-palette colors (useful for Add Hotcue Color Replace Dialog #2547)

[Holzhaus]

@Holzhaus Merge? I need this for #2547, just split it off to the PR reviewable and small.

[uklotzde]

LGTM

[Be-ing]

Why is the custom color button not enabled anywhere? I don't think there's a need to make it optional, just enable it. What is the need to hide it in any case?

[Holzhaus]

The already support largest, custom palettes. There is simply no need to open a full-blown QColorDialog when assigning a cue color.

The custom color button will be used for the color replace dialog, where it makes sense to allow picking arbitrary colors.

[Be-ing]

Consider a user experimenting with adding another color to their palette but they aren't sure exactly what color they want that to be yet. Currently this user would have to go into the preferences to edit the palette, switch to the main window, right click the hotcue and click the new color, and repeat this for every small adjustment to the color. This would be easier if they could access the color picker directly from the cue menu.

Or maybe a user has some reason for setting a specific hotcue to a color they rarely use. Anyway, the code is already implemented, there is plenty of screen space available for the cue menu, it gives the user much more flexibility, and does not increase the complexity of the code. I don't think there's a good reason to hide the custom color button.