Display alert when no occurrences to review for disease

- Per disease group, compare the total number of occurrences with number of expert's reviews. If these values match, there are none in need of review by user. Create and return a hashmap for each count, to easily add to the javascript disease object.
- Also in the controller, mock up the same hashmaps for the default disease (dengue) for when user not logged in.
- Freemarker maps only support string keys, so the disease group's display name was used instead of id.
- NB. Currently occurrenceCount is <i>all</i> occurrences in DB for disease group when in actuality this set should be refined to only return the <i>questionable</i> occurrences (when the flag exists).