12-factorize application a little

snikket_web can now be fully configured via the environment alone,
no extra files needed. It is still supported to inject a python
file to generate environment variables though, which may be
useful for generating and reloading a secret key.

.envrc

@@ -2,4 +2,4 @@ layout python3
 
 export QUART_APP='snikket_web:create_app()'
 export QUART_ENV=development
-export SNIKKET_WEB_CONFIG="$(pwd)/.local/web_config.py"
+export QUART_DEBUG=1