Add Maven Archetypes for skeleton projects

It's a good idea to have a template for new projects to help users adhere to best practices for project layout.

Provides:

  * A Java Archetype, `java-simple`, for creating new Java Dropwizard projects.
  * A Scala Archetype, `scala-simple`, for creating new Scala Dropwizard projects. [update: **no Scala support as of 0.7.0**]
  * A utility, `dropwizard-create`, for bootstrapping a new project using the Archetypes.

The POM for generated projects will:

  * Generate JavaDoc/ScalaDoc, and build an attached doc JAR.
  * Build and attach a source JAR.
  * Build shaded JAR (optional)
  * Build an executable JAR for the Service.
  * Generate Maven Site

The `dropwizard-create` utility is provided so that users don't have to grapple with Mavens' appalling UI for generating projects from Archetypes. It ensures that all the necessary properties are provided to
the Archetypes and provides some sensible defaults for the lazy.