Searching maps and groups by URL

Currently, when you go to the maps page and search for a location, then reload the page, you’re given a blank maps page. The same scenario happens on the groups page, when listing all groups.

This branch makes it possible to reload the page and be taken back to the same page. Additionally, the map/groups link can be shared with another person and they can see the map or group with the same search.

This branch also refactors the Open Street Map code, so check that the OSM tiles are still appearing correctly on the map page and the groups map.

Also check that the page is behaving correctly on the group map page as well as the whole-site map.