Restructure and add features

[mhaulo]

This pull request is a combination of three commits. Two of them are fairly big changes.

The motivation behind these changes was to create features for drawing GeoJSON shapes on top of a base map. This added some complexity, and to keep the codebase tidy, I decided to make some structural changes first. For implementatio details, please see individual commit messages.

In general, this seems to be working quite nicely. But I'd be surprised if I hadn't made any mistakes, so it would be great to have someone else test this thorougly as well.