Fix discovery JSON

The image should always link to <domain>/user.jpg.
Change bundled database.yml to use DATABASE_URL in production. (closes #11)
Update '.gitignore'
Change 'config/deploy/production.rb'
Remove appsignal stuff
Don't use S3 datastore
Deploy from fork repo
Set correct Ruby version
Don't use chruby
Use 'capistrano/rbenv'
Fix dotenv config

We don't use 'dotenv-deployment' for production because it doesn't work
for our setup.
Remove turbolinks crap
Fix `deploy:restart` capistrano task
Don't display "Login" link
Put 'quiet_assets' gem into `:development` group
Put 'puma' gem into `:staging, :production` group
Remove 'rack-cache' gem
Load fonts from the very same host
Remove autofocus stuff
Remove publish form on network page