Using maven-metadata.xml instead of Lucene Indices

I changed literally everything except the plugin name to remove Lucene from the equation. This pull request:

- fixes issues #3, #15 and probably #9, realizes enhancement #11 (since Lucene is no longer used)
- fixes issues #4, #7, #10, #13 and probably #8
- enables checking of plugins (using `:plugins`) on the command line, thus probably resolving issue #14

I hope this pull request matches your expectations. I'm definitely looking forward to your comment.