Unzip mirah-util into dist/classes so that MirahCommand gets also packaged.

`MirahCommand` is now put in a separate jar, mirah-util.jar which does not
get merged into mirah.jar and mirah-complete.jar.  This fix is a temporary
workaround to package `MirahCommand` into the generated jars so that the
maven-mirah-command plugin works again.  I am working on a more “Maven-like” approach.