1) The full text search was looping over the DiveListModel when
it could simply loop over the core model. Do that instead.
2) Don't generate a DiveObjectHelper to do a full text search.
Currently this is harmless as the DiveObjectHelper is only
a disguised "dive *". But from a conceptual point of view,
it represents the full representation of a dive and we don't
want to generate that in a tight loop.
This will help in
1) Making the DiveObjectHelper a non-reference object.
2) Moving fulltext search to the core and thus making it available
to desktop and more performant.
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>