add a User.get classmethod that returns an instantiated User object

[highflyingaction]

Having to populate a User object with the data returned from Yola().get_user() is annoying, especially since the service returns signupDate and the model expects that attribute to be named signup_date.

Let's use this new User.get() method so we never have to deal with that again.

[snitch]

:sparkles: No lint errors found. :sparkles:

[blaix]

👍