Add support for other administrative areas

I noticed that if an area is two tier, only the first authority (usually the district) is returned. This PR adds support for two tier authorities, other administrative areas, easting and northing, as well as Rspec tests.

I also noticed that the x and y coordinates were the wrong way round, so fixed that too - I think the confusion comes from the fact that Mapit expects queries in the format y,x, as opposed to the more traditional x,y.

Thoughts welcome! :smile: