Protected Areas API

Creates a API to query by wdpa_id (to feed third party projects on protected-planet-consumer)

The query can be done using:

http://localhost:3000/api/protected_areas?wdpa_id=[wdpa_id]

You can check the code on

controllers/api/protected_areas.rb
models/protected_areas.rb
test/integration/api_test.rb

Looking at this again, I realise we should make this RESTful. Use a namespace and resource:

```
namespace :api do
  resources :protected_areas, only: [:show]
end
```