Add the data map to the storybook

[eatyourgreens]

Having the data map in the storybook would be useful for either building new map layers (#8), or adding new features to existing layers (#126.) It would also give us a sandbox for testing refactors to the data loaders (#159.)

I think a working story for the data map would involve either of the following:

• building some mocks for the data API and map tiles.
• connecting the storybook to the existing API, so that you authenticate in order to interact with map data.