Update dependencies

[Filienko]

Added tests and updated dependencies to support newer Python version

Major changes:

With newer pyjwt library, the jwt.encode() function returns a string instead of a byte object.
JSONEncoder is changed to DefaultJSONProvider
and app.json_encoder = JSONEncoder to the app.json = YourJSONProvider(app)

[pbugni]

Only concern is requrements.dev.txt - shouldn't that import the base via -r requirements.txt rather than repeat?