Replace how .load is called

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.

app/notifications/rest.py

@@ -48,7 +48,8 @@ def get_notification_by_id(notification_id):
 
 @notifications.route('/notifications', methods=['GET'])
 def get_all_notifications():
-    data = notifications_filter_schema.load(request.args).data
+    data = notifications_filter_schema.load(request.args)
+
     include_jobs = data.get('include_jobs', False)
     page = data.get('page', 1)
     page_size = data.get('page_size', current_app.config.get('API_PAGE_SIZE'))
@@ -83,13 +84,10 @@ def send_notification(notification_type):
         msg = msg + ", please use the latest version of the client" if notification_type == LETTER_TYPE else msg
         raise InvalidRequest(msg, 400)
 
-    notification_form, errors = (
+    notification_form = (
         sms_template_notification_schema if notification_type == SMS_TYPE else email_notification_schema
     ).load(request.get_json())
 
-    if errors:
-        raise InvalidRequest(errors, status_code=400)
-
     check_rate_limiting(authenticated_service, api_user)
 
     template, template_with_content = validate_template(