Query: Added utilities class to interrogate available filters.
Updated web services and akka-workers to work with new filter listing.
Added ability to print list of installed filters from command line client.
Annotated other packges that provide query filters.
Removed old service helper class (for listing filters).
Query: Getting a list of filters is now more robust.

Instead of listing every filter in a metadata file in an
unrelated directory, simple create an empty file called
`filter-pack.cfg` in the package directory. Any classes that
belong to that package and implement the `Filter` interface
will be automatically picked up and listed in the
/QueryFilter.xml web service.

Also added a `filter list` command to the command line client
to get the same information.

Merge branch 'feature-dynamic-filter-list' into akka-workers