Update style guide to include standard colors for common use cases

[mitchelljkotler]

Related to issue #1829, we'd like to have some standard accessible palettes we can use for various charts. Examples below and TK.

These should align with broader MuckRock branding, and be in use for both automated visuals (muckrock.com/place) as well as new one off interactive.

Use Cases:

• Two or more comparative states, such as mapping good, mediocre and bad on our place map or yes and no on an exemptions map.
• Gradations such as pollution levels across states.

Ideally our style guide would say "So you have categorical data in 3 buckets, these are your options" or "You need a sequential color palette for 5 colors, try these" based on the 5-10 core colors we choose. Lisa Charlotte Muth has a good Datawrapper blog post on choosing colors for a style guide and the Data Vis Society has a decent spreadsheet of data vis style guides.

MuckRock's current style guide is here, with internal branding guidance and some CMS information which touches on style guide issues.

@DillonBergin contributed to the above and has also offered to be a resource as needed.

[allanlasser]

@morisy @mitchelljkotler

Here is a first pass on an accessible color matrix. I'll address any feedback here, then update the linked documents (I think I need the branding and CMS documents shared with me).