return new archived flag on change

- publish event on archived state change
implements fulltext search via lucene (close #2)
fixes SearchActor and tests

Fixes SearchActor to not access `sender` within a future. Creating child
actors on demand must be thread-safe, since rebuild-actor uses it, too.

The tests involving mongodb were running unreliably; they occassionally
threw errors. This attempt now uses the same db for all tests and
requests sequential processing which seems to solve this.