Ensure that dependent projects (and our own) jars are created when
making a JavaApp distribution.  We use the dependency-classpath in Runtime
to determine classpath ordering, but we pull jars directly from the
packagedArtifacts keys of dependent projects.  Uses a bit of
advanced sbt hackery.

Fixes #19

However, this introduces an error in the scripts I'm looking into.
Will squash this commit with further fixes.