Add api bootstrap

 - Adds model and controllers by generate the api structure.

Signed: Uriel Molina<uriel85@gmail.com>
Create migrations and models for endpoint

Signed: Uriel Molina<uriel.molina@diverza.com>
Remove empty migration

Signed: Uriel Molina<uriel.molina@diverza.com>
Create response on json for cities and countries

 - Removes foreign key on cities, for conflict on id.
 - Change wrong field name contry for country on table countries.

Signed: Uriel Molina<uriel.molina@diverza.com>
Add pollutants_agents service.

Signed: Uriel Molina<uriel.molina@diverza.com>
Add stations service

Signed: Uriel Molina<uriel.molina@diverza.com>
Merge pull request #9 from chirakiru/api-v1

Api v1