feat: add summary of impact page (resolves #35)

[greatislander]

• [x] I've read the guidelines for Contributing to the Platform Co-op Toolkit
• [x] This isn't a duplicate of an existing pull request

Description

Adds MVP implementation of the Summary of Impact page.

TODO:

• [x] Country segmentation
• [x] Organization type switching
• [x] Geo scope chart
• [x] Styling

Steps to test

1. Visit /about/impact/.

Expected behavior: Page matches https://github.com/platform-coop-toolkit/coop-map-directory-index/issues/35#issuecomment-651923178.

Additional information

Not applicable.

Related issues

Resolves #35.

[greatislander]

@cherylhjli @dayotte would like to review this with you on Monday. I would also like some accessibility feedback on the chart from @jhung if possible.

[greatislander]

Merging and deploying for easier review.