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
Here I got the dreaded
```
-----> Fetching custom git buildpack... done

 !     Push rejected, no Cedar-supported app detected
```
Even after I set my buildback url:
```
(bpz)lcrouch-14912:BPZAround.me lcrouch$ heroku config
=== bpz-groovecoder Config Vars
BUILDPACK_URL: https://github.com/ddollar/heroku-buildpack-multi.git
```
I wonder if we need to push the code up to heroku a first time so it has the `.buildpacks` file for the first build with `postgis://` ?