Support native MongoDB queries

[andyjefferson]

We could potentially allow
pm.newQuery("MongoDB", "db.MYCOLL.findOne({'_id':'" + oid + "'})");

em.createNativeQuery("db.MYCOLL.findOne({'_id':'" + oid + "'})", MyClass.class);

Obviously this would have to only support a subset of the possible MongoDB API calls possible from DB.getCollection(...). So find, and findOne. Similarly the returned DBObject's would need unmapping to return the Object[] for a row of results.

The alternative is already available via NucleusConnection