While beginning to develop maps features, we've identified a few ideosyncracies which make kartotherian development more difficult than it needs to be. We'll attach work to this epic at it comes up.

In addition to the subtasks, it would be nice to:

• Catalogue custom (WMF-owned) dependencies
• Make sure nothing remains in the archived GitHub kartotherian project.
• Un-fork as many components as possible.

Some specific changes which didn't end up with their own subtasks:

• Update linters to the newest versions still supporting node 10: 4ecd5d8c, 69f96d25, 22e0fae7, eed7e2aa, b0ac04f, b3ff075
• Replace some promises with async/await: e5b4c51eaeb0
• Refactor geoshapes as pure functions: e5b4c51eaeb, 68315c9e, a98c7cf0ef, 5d9f4b4, 0be461e5, a92ad93fb