Fix some date/time functions and add new helper functions

aleksis/apps/chronos/models.py

@@ -68,7 +68,7 @@ class TimePeriod(ExtensibleModel):
             year = date.today().year
             week_number = week or getattr(self, "_week", None) or CalendarWeek().week
 
-            if week_number < SchoolTerm.current_term.date_start.isocalendar()[1]:
+            if week_number < SchoolTerm.current.date_start.isocalendar()[1]:
                 year += 1
 
             wanted_week = CalendarWeek(year=year, week=week_number)