4 - create GET /stats/failuresByStates

[glmaljkovich]

Create an endpoint that lists the failures by state. In order to make it simpler you don't have to count how many failures a student has. It means each student count once even if he/she fails more than one exam.

route: /stats/failuresByStates
method: GET
params: none
response: {data: {<state>: Number}}
responseExample: { data: { "California": 2, "Buenos Aires": 1 } }