add some missing api public method needed by the Jira Bridge tests an…

…d fix some wrong data type (#332)

shotgun_api3/lib/mockgun/mockgun.py

@@ -425,6 +425,12 @@ def upload(self, entity_type, entity_id, path, field_name=None, display_name=Non
     def upload_thumbnail(self, entity_type, entity_id, path, **kwargs):
         pass
 
+    def add_user_agent(self, agent):
+        pass
+
+    def set_session_uuid(self, session_uuid):
+        pass
+
     ###################################################################################################
     # internal methods and members
 
@@ -497,8 +503,9 @@ def _validate_entity_data(self, entity_type, data):
                                    "text": six.string_types,
                                    "serializable": dict,
                                    "entity_type": six.string_types,
-                                   "date": datetime.date,
+                                   "date": six.string_types,
                                    "date_time": datetime.datetime,
+                                   "duration": int,
                                    "list": six.string_types,
                                    "status_list": six.string_types,
                                    "url": dict}[sg_type]