Disease extent generation now uses contemporary occurrence points

Disease extent generation now uses only the latest occurrence points, like the model does, if automatic model runs are on. The permutations are as follows:

If automatic model runs are off:
1. Update weightings and isValidated
2. Create/update disease extent
3. Get occurrences for model run
4. Run model (if enough occurrences)

If automatic model runs are on, then before model run:
1. Get occurrences for model run
2. Create/update disease extent, with a minimum occurrence date set by step 1
3. Update weightings and isValidated
4. Get occurrences for model run again
5. Run model (if enough occurrences)

If automatic model runs are on, then after model run:
1. Get occurrences for model run
2. Create/update disease extent, with a minimum occurrence date