Added new colors to theme

[Douglashdaniel]

Changes

Resolves https://github.com/brave/brave-ui/issues/584

Added new colors 'excluding gradients' from the design team to the brave-default and brave-dark themes.

Link / storybook path to visual changes

Integration

• [ ] Does this contain changes to src/components or src/

  • [ ] Will you publish to npm immediately after this PR, or wait until sometime in the future?
  • [ ] Incompatible API change to something existing (major version increase)
  • [ ] Adding new backwards-compatible functionality? (minor version increase)
  • [ ] Fixing a bug backwards-compatibly? (patch version increase)

• [ ] Does this contain changes to src/features for brave-core?

  • [ ] Are there non backwards-compatible changes required for brave-core? Do not merge until brave-core PR is approvable. Link to brave-core PR:
  • [ ] Will you create brave-core PR to update to this commit after it is merged?
  • [ ] Wants uplift to brave-core feature branch?
    • When uplift-approved, merge to brave-core-0.VV.x feature branch
    • Create additional brave-core PRs for each feature branch to update commit