Make iD default editor

This makes iD the default editor on OSM. It's already the first option in the drop down, but this PR makes iD the editor that users land in when they just click the "Edit" label.

I hope to get this merged, now that [initial concerns](https://github.com/openstreetmap/openstreetmap-website/pull/262) were addressed with the 1.1. release of iD [that was just rolled out on OpenStreetMap.org](https://github.com/openstreetmap/openstreetmap-website/pull/424):

- Improved performance
- Added relation support