Add an overpass based query tool

This pull adds an overpass based query tool. A new icon on the right hand side of the map activates query mode where clicking on the map will ask overpass for both "nearby" and "enclosing" features and display the resulting lists in the side bar.

There are a few things that I no need to be resolved before this is merged:

- [ ] Need a better icon for the tool
- [ ] Work out what to do about https

Comments, criticisms, code reviews etc welcome...