Added subdirectory for address addition

Fixes #5.

Originally, the goal here was to allow people to add their residences, but I've made the language generic enough so that we could be dealing with any address.

The `address` subdirectory creates a place for users to add their address to OSM if it's missing.

The `index.html` is pretty much a clone of the existing one, with form fields changed/removed.  The major tweaks in `site.js` are just to check whether we're on the original `index.html` or the new one.

I'd like to get feedback from @iandees and @tmcw about whether additional fields/tags should be added, the main one being `Category` like you have for the original onosm.org