Geokey-dataimports

Add Python 3 compatibility. Maintains Python 2 support.

Couple fixes:
- fixed importing numeric values when field type is set to "text"
- fixed re-selecting features on the map when deciding what to import

Added support for Django 1.11 (with GeoKey 1.6).

This patch only adds documentation on how to run geokey-dataimports when running GeoKey within a Docker container.

Patch fixes deployment to PyPI and adds package description to the registry.

Patch fixes importing GeoJSON files.