Update colors

[magicznyleszek]

Checklist

1. If you've added code that should be tested, add tests
2. If you've changed APIs, update (or create!) the documentation
3. Ensure the tests pass
4. Make sure that your code lints and that you've followed our coding style
5. Write a title and, if necessary, a description of your work suitable for publishing in our release notes
6. Mention any related issues in this repository (as #ISSUE) and in other repositories (as kobotoolbox/other#ISSUE)
7. Open an issue in the docs if there are UI/UX changes

Description

We've updated most of the colors in our palette to more accessible shades, and added few new colors in preparation for upcoming improvements.

Notes

Most of the colors were slightly updated. We had a major change in reds:

• kobo-red was renamed to kobo-mid-red
• kobo-dark-red was renamed to kobo-red (this is the part that might be confusing)
• we have new kobo-dark-red that is slightly darker

Another big change was with grays:

• All kobo-gray-<lightness number> were renamed to kobo-neutral-<counter>, e.g. kobo-gray-98 is now kobo-neutral-100
• We use -100, -200, -300, …, -900 as neutral color "types". This allows us to have flexibility of adding -250 in future if needed
• The shades of neutrals were updated too

Other changes here:

• Migrated Button dark-red to red (this is kinda undoing recent change, but previous change Update red Buttons to use dark-red for accessibility #4993 was changing the color to darker shade, this one keeps the color, but the name is different)
• Migrated Icon component from red to mid-red
• Removed duplicated lines of code from react-tagsinput.scss file (I'm pretty sure I already did that)
• Updated the reds being used in various places to ones that make sense. Some were left as kobo-red (so will be darker than previously), and some were updated to be kobo-mid-red (so will appear as if nothing changed)

Related issues

Followup to #4993
Made kobotoolbox/docs#372

[duvld]

I did a quick look around the UI and it looks like your find and replace got all of them :) if someone spots a missed spot we can probably do individual touch ups