Usertoschool

When getting a user from the User API, it's school field is now a school object. Had to adjust the serializer for school and user. Also needed to adjust unit tests because the registered field of school had to be changed from a datetime.datetime (because it couldn't json serialize) to a string in the iso-8601 format. Also needed to adjust the unit tests to handle a school object for the school field of a user for the user get cases.