Add Map Delete Button to Resume Page

Also, add JSON import/export buttons on the createmap page. There are still quite a lot of TODOs I added and haven't done yet, but the delete functionality and changes to createmap should be fully operational. Please let me know how this looks so far.

This branch is not compatible with existing badgerdb's - it creates indexes for stored objects and relies on them for deletion (and for showing all maps on the resume page). Existing games might sort of work but the /maps/all endpoint won't know about them. Might be good to add some kind of versioning and version check (maybe even a migration script) but I'm lazy.

Resolves #65