Add config option to map values to colors

[lukasolson]

Closes #4817.

This PR adds a config option that allows users to associate colors with specific values, and defaults Count to be the standard green, so that it's not mapped to different colors based on the context of the application.

[BigFunger]

A couple of things:

• This doesn't maintain a unique list of colors for a visualization.
  • I took a visualization, and found out the color that was being used by default for the second line.
  • I added a config value to make that the color for the first line.
  • The visualization now uses that color for both lines.
    
• this doesn't watch for changes in config, so the user must do a hard refresh to apply the colors
• the variable name colorMapping for the config values was confusing to me in the context of the code when there is already a mappedColors variable. Purely subjective.

[lukasolson]

Okay, so I made some pretty drastic changes.

I moved the logic that maps colors from color.js to mapped_colors.js. I also modified the latter file to return a singleton instead of a class that needs to be instantiated (I anticipate that only one instance will ever be needed). Prior to these changes, mapped_colors was essentially just a set, but now it has some important functionality that checks the colors mapped by the user's config, and picks colors that the user hasn't already used in the config.

[tsullivan]

nitpick - kind of inconsistent here in that you use fat arrow syntax in other new code

[tsullivan]

LGTM - other than those 2 things

[lukasolson]

Passing to @rashidkpc for a quick final look.

[rashidkpc]

This LGTM, it also provides a work around for users that need custom color, albeit global, until custom color palette support is in. Eg, setting success to green, errors to red

[seshukumaradiraju]

Tried this and have one issue.
Gave Success color as green and error as red.

When data has both categories .. the colors are shown correctly.

But when I zoom in where only errors are present, color changes to green.

Any fix/workaround for this?