Add the timezone property to app

It will make it easier to get a default time zone.

calsocial/models.py

@@ -111,19 +111,18 @@ class User(db.Model, UserMixin):
     @property
     def timezone(self):
         from flask import current_app
-        from pytz import timezone, UTC
+        from pytz import timezone
         from pytz.exceptions import UnknownTimeZoneError
 
         timezone_str = self.settings['timezone']
 
-        if not timezone_str:
-            timezone_str = current_app.settings.get('DEFAULT_TIMEZONE', 'UTC')
+        if timezone_str:
+            try:
+                return timezone(timezone_str)
+            except UnknownTimeZoneError:
+                warn(f'Timezone of {self} (or the default timezone) "{timezone_str}" is invalid')
 
-        try:
-            return timezone(timezone_str)
-        except pytz.exceptions.UnknownTimeZoneError:
-            warn(f'Timezone of {user} (or the default timezone) "{timezone_str}" is invalid')
-            return UTC
+        return current_app.timezone
 
     def __repr__(self):
         return f'<User {self.id}({self.username})>'