1. All services are disabled in testing now to prevent network accesses
2. Only services are enabled when needed to test something
3. Many changes throughout code to allow iD to run with services disabled
(e.g. check for osm service instead of assuming context.connection() will work)
4. Actually export the services so we can disable and enable them
- Cache vintage lookups from Bing API
- Actually sample a tile at the center of the viewport,
rather than just divinding tiles/2 (not a good guess)
- Refactor the start-end range code into one place
