Move the AppHelper file in into the right directory
Add initial support for defining and validating migrations
Wire the dropwizard-flyway code into the main application for running migrations, etc
Run the Flyway migrations inside of the StubAppRunner to ensure we come up with a DB

I had originally put this inside of the AppHelper code but that codepath is
executed in a different classloader environment which results in the H2 named
in-memory database being created twice, once in the cukes and again inside of
the Dropwizard application.

This will probably need to be refactored at some point, but for now it gives us
the same in-memory DB in both places
Return a 404 if we cannot find the artifact in the database

This commit starts wiring the ArtifactResource into an actual configured
database (in-memory H2 for now)
Documentation update for the latest groovy and rest docs