https://marshmallow.readthedocs.io/en/stable/upgrading.html#schemas-are-always-strict
`.load` doesn't return a `(data, errors)` tuple any more - only data is
returned. A `ValidationError` is raised if validation fails. The code
now relies on the `marshmallow_validation_error` error handler to handle
errors instead of having to raise an `InvalidRequest`. This has no
effect on the response that is returned (a test has been modified to
check).
Also added a new `password` field to the `UserSchema` so that we don't
have to specially check for password errors in the `.create_user` endpoint
- we can let marshmallow handle them.
or param errors to raise invalid data exception. That will cause
those responses to be handled in by errors.py, which will log
the errors.
Set most of schemas to strict mode so that marshmallow will raise
exception rather than checking for errors in return tuple from load.
Added handler to errors.py for marshmallow validation errors.
