Use static import of directives in Java docs

For example here http://doc.akka.io/docs/akka/2.4/java/http/routing-dsl/overview.html
the samples are gaining access to the directives by inheriting (I'm guessing a Scala person wrote this, as mixing in functionality is not uncommon in Scala land). I think this is confusing for Java developers who mostly see inheritance as _is-a_ which doesn't fit at all here, and that we should make sure the Java samples use a static import of the directives instead.

Start with the Java HTTP routing DSL overview at the linked documentation URL and inspect how the samples access directives through inheritance. Update the samples to use static directive imports instead; done means the Java examples no longer inherit directives for this purpose and remain understandable to Java developers.

Written by the indexing model from the issue text.