Disallow cumulative markers for overlapping datasets

We should add an extra field _allow_cumulative_markers_ for datasets.

This field should be false except for these datasets:
- 2 ASIA Events
- 3 IRIS Claims
- 12 Decidim PAM Meetings
- 14 DDDC Meetings

Then, main.js should be updated to only show the cumulative option when (1) the selected visual model is _map_, and (2) the selected dataset is one from the above list.