Flask required only if necessary (#424)

* Example with Flask support

* Only show import error when trying to use Flask

* Re-organize imports

* Move flask_utils next to related module

* Code style

* Change back to incentivizes

* Includes Flask by default

* Project clean up

* Update Rafael Caricio's e-mail address

* Fix conflicts

tests/api/test_parameters.py

@@ -1,6 +1,7 @@
 import json
 from io import BytesIO
 
+
 def test_parameter_validation(simple_app):
     app_client = simple_app.app.test_client()