Merge branch 'add_basic_queries' into 'development'

Implement basic queries for enrollments

# Description

Implemented enrollments queries per:
- Region
- State
- City

The *census_year* parameter is *mandatory* and should be included in all requests.

The "/enrollments" route supports the following parameters

- aggregate: metric to aggregate, can be {state, region, city}. When no parameter is supplied or the parameter is not supported, the API assumes the whole country.
- id: record identifer of the metric to aggregate (e.g. one specific state or region), it only applies when the aggregate parameters is passed and is valid. Again, when no parameter is specified, the API assumes the whole range of values the metric can take (e.g. all states or all regions).
- adm_dependency_id: administrative dependency identifier, the possible values are shown in the Table 1.

- location_id: location identifier, its possible values are given in Table 2.

# Tables

*Table 1:* Administrative dependency table.

| adm_dependency_id | name           |
|---------------------------|---------------|
| 0                                          | All records  |
| 1                                          | Federal        |
| 2                                          | Estadual     |
| 3                                          | Municipal   |
| 4                                           | Privada       |

*Table 2:* Location table.

| location_id  | name            |
|----------------|---------------|
| 0                        | All records  |
| 1                        | Urbana        |
| 2                        | Rural            |

# Response Format

The API returns a JSON array with name "result" where every array has following attributes:
- name: Name of the metric (e.g. name of a state, city or region)
- total: Total number of enrollments for the selected metric and given parameters.

# Examples
Retrieve the number of enrollments of 2014 for the whole country:
> /api/v1/enrollments?census_year=2014

Retrieve the number of enrollments of 2013 for a given region:
> /api/v1/enrollments?census_year=2013&aggregate=region&id=1

Retrieve the number of enrollments of 2012 for all rural locations in the state of Paraná:
> /api/v1/enrollments?census_year=2012&aggregate=state&id=41&location_id=2

Retrieve the number of enrollments of 2012 for the North region:
> /api/v1/enrollments?census_year=2012&aggregate=region&id=1

See merge request !5