Radius and refactor

Exposed the radius property of the buildings API through all of Building Grabber.
Extracted the whole building grabber functionality into its own class.
Renames some stuff to be more consistent.

First Release

The initial release of building grabber.

There are three known issues with this first release:

1. Currently, any polygons will only grab buildings along the edge of the first ring of each polygon. In a multi-polygon, the same will happen for each polygon.
2. The input geojson file requires the geometries to be contained in a feature collection.
3. Adjusting the radius of the search is not exposed through run.py