Add User.employee convenience attribute.

rattail/db/model/users.py

@@ -120,6 +120,14 @@ class User(Base):
             return self.person.display_name
         return self.username
 
+    @property
+    def employee(self):
+        """
+        Convenience attribute to fetch a reference to the connected
+        ``Employee`` instance, or ``None``.
+        """
+        return self.person.employee if self.person else None
+
     def get_email_address(self):
         """
         Returns the primary email address for the user (as unicode string), or