Assign correct endpoint to each resource instance

[multimeric]

By default we assign each Resource class with a view/endpoint. However if the same resource is used for multiple routes, the endpoint will be overwritten.

e.g. previously this test would fail:

    api = Api()

    class DummyResource(ResourceDetail):
        def get(self):
            return self.view

    api.route(DummyResource, 'endpoint1', '/url1')
    api.route(DummyResource, 'endpoint2', '/url2')
    api.init_app(app)

    with app.test_client() as client:
        assert client.get('/url1', content_type='application/vnd.api+json').json == 'endpoint1'
        assert client.get('/url2', content_type='application/vnd.api+json').json == 'endpoint2'

[coveralls]

Coverage increased (+0.06%) to 90.83% when pulling 01d2847 on TMiguelT:resource_view into b44bc08 on miLibris:master.

[coveralls]

Coverage increased (+0.06%) to 90.83% when pulling fbf28cd on TMiguelT:resource_view into b44bc08 on miLibris:master.