Allow mixed method for cohort and obs

There is no easy way to produce a report which breaks down observations by patient demographics. Create a simple way to report by gender, age and some other dimension (ie. coded diagnosis).

Attached is an example of a Haiti MoH report. See page 3 and 4 for the list of diagnoses with subtotals by gender and age. For this example with 50+ diagnoses, it is necessary to create 50 dataset definitions with mapping to the different diagnosis concept.