Implement matriculas in the API

Implement the following aggregations:
- per-state
- per-region
- country

In order to use these queries one should use the /api/v1/matriculas route. When
the 'agregar' query parameter is set, one could use the values 'estado' and 'regiao'
to run the aggregation for state and region, respectively. Otherwise, if no parameters
are supplied, it defaults to the whole country aggregation query.