Display metadata fields sorted in QueryTool
Fixed some Javadoc comments
Some more structural improvements to Searcher and Hits.

- moved methods that take a Hits object from Searcher to Hits
- turned static methods in Hits that take a Hits object into
instance methods
- inlined short private methods that were only called once
Made HitsWindow copy Hit objects.

Before it referenced them, but that can cause problems when overwriting
the context[] array of the objects (since it belong to two different
collections, one Hits and one HitsWindow).

Hit is now cloneable and HitsWindow clones the Hits it's interested in.
This shouldn't be a problem as HitsWindow is usually used with small
(max. ca. 100) numbers of hits.
Added and updated Javadocs