Update `Dockerfile`; more logging and test fixes

* Update the `Dockerfile` with the new build command.
* Add a `-version` flag.
* Log all `http.Server` errors.
* Add `ApplicationConfig.{ResolveHost, Origin}` to support running the Python smoke tests from a separate Docker container.
* Normalize the `RequestHeader.Type` case. This was a regression caught by the smoke tests.

@jrconlin r?
I should submit jrconlin/simplepush_test#4 against that repo, then.