Improve Query Caching - this prevents creating multiple instances of the...

... same query

The change makes sure, that for each Query of this repository only exactly one instance is present at any time. Before this change the RedmineQueries were recreated on earch call to RedmineRepository#getQueries - with this change this is prevented and the queries are deserialized only once and then the backing store and the runtime Querymap (RedmineRepository#queries) are updated together.
make `final`?