Make sure starting an Https server is well documented for Java DSL too

**Issue by [ktoso](https://github.com/ktoso)**
_Tuesday Mar 29, 2016 at 08:11 GMT_
_Originally opened as https://github.com/akka/akka/issues/20154_

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See this discussion: https://twitter.com/ktosopl/status/714725071206617091?cn=ZmF2b3JpdGU%3D&refsrc=email

Seems `HttpApp` is somewhat hurting us and concealing that it's actually pretty similar to Scala DSL.
This should be done after new DSL merged; Perhaps deprecating HttpApp?

Start by reviewing how HTTPS server startup is documented for the Scala DSL and how the Java DSL currently exposes HttpApp. After the new DSL is merged, document the equivalent Java DSL setup and determine whether HttpApp should be deprecated, as suggested in the issue.

Written by the indexing model from the issue text.