Get heroku manual build working

[jwhitlock]

• 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

[groovecoder]

I'll try to run thru the instructions myself later today.

[groovecoder]

Nit-pick: Can we drop the $ characters from the command-line blocks? That way I can triple-click the lines to copy and paste them.