Parametrize client_max_body_size / client_body_timeout

[bcardiff]

The default values for client_max_body_size / client_body_timeout in nginx are a bit limited (1M / 60s).
It would be great to increase them in the template or even better allow an env var to define it's value.

https://github.com/jwilder/dockerize could be used to expand template files for config on boot time