Weighting fixes

1. Set machine weighting to null if environmental suitability and distance from disease extent are both null (in DiseaseOccurrenceValidationServiceImpl)

2. Ensure nulls are ignored when calculating average (in WeightingsCalculator)

3. Only set final weightings for occurrences which don't yet have a final weighting (in WeightingsCalculator - uses new query getDiseaseOccurrencesYetToHaveFinalWeightingAssigned)

4. When calculating final weighting, if validation weighting is null and ES is not null, set the final weighting to location resolution weighting (which must be not null) and the final weighting excl spatial to 1.0 (in WeightingsCalculator)

5. Requesting a model run should exclude occurrences where final weighting is null (in ModelRunRequester - uses amended query getDiseaseOccurrencesForModelRunRequest)

6. GeoJsonDiseaseOccurrenceFeatureProperties should use final weighting not validation weighting. Changes through the tests, and added final weightings to disease occurrence test data.

NB. JIRA195 doc in Sprint Management on GoogleDrive might help clear up what has been implemented and how it has been tested!
Neat solution :)