Allow the transport of datetime and date objects over WAMP

[zaberblake]

Currently, datetime and date objects are not natively JSON serializable and thus are not transportable over WAMP. By overwriting the default() method of json.JSONEncoder we can specify the encoding behavior of datetime and date objects. Using isoformat(), we can thus standardize the behavior of dates sent over WAMP which allows us to do cool things such as automatically parsing dates into datetime objects using fromisoformat().