implement color picking from predefined set for category badges + option to change foreground color

[kubamracek]

This is a pull request to implement this:

Basically, it's just adding an option to change category badge foreground color the same way that you can change background color. Plus 16 predefined colors to select from. I felt that implementing a true-color palette was too much trouble, so I implemented just this.

Let me know, how you fell about this, of course the 16 colors are pretty much random and we can change always them. Comments and critics is welcome.

[discoursebot]

You've signed the CLA, kubabrecka. Thank you! This pull request is ready for review.

[ZogStriP]

This is excellent! 😉

A few suggestions:

• Wouldn't it be nicer if the text of the category was binded on the preview tag?
• Color's textbox should have rounded corners to match the style of the rest of the application (missing a class?)
• Have you tried implementing this color picker?
• The predefinedColors array should be a Site Setting

[eviltrout]

We ove this! Merged 🐟

We can try the suggestions in future PRs!

[coding-horror]

This is excellent, and thank you so much! Merged for testing, and so far so good!

Some additional things I would like to see

• Important: we really only want to offer black and white text, I feel like we are overloading people with too much choice (and the potential for very very ugly choices) if they can set text colors other than simple black or white...
• We should show which colors are already in use by existing categories marking the colors? Perhaps putting a dot on the ones that are in use or some other marker?

A designer we worked with did provide this list of default category colors, so let's try to add that, it is DESIGNER APPROVED! 😉

Yet again thank you this is a great contribution that makes it so much easier to pick non-insane category colors for everyone 👍