Get heroku manual build working

- Remove "Deploy to Heroku" button, since no free option
- Uses https://github.com/cyberdelia/heroku-geo-buildpack.git
- If Heroku detected, database driver switched to postgis
- Retain staticfiles folder for working ./manage.py collectstatic
- app.json has the minimal config for DEBUG=False config, loads data
- Closes #50
At this point I got:
```
django.core.exceptions.ImproperlyConfigured: Cannot determine PostGIS version for database "bpzgroovecoder". GeoDjango requires at least PostGIS version 1.3. Was the database created from a spatial database template?
```