free coach has pro if four pro athletes

rowers/models.py

@@ -651,6 +651,10 @@ class CoachingGroup(models.Model):
             id = self.pk,
             name = self.name
             )
+
+    def __len__(self):
+        rs = Rower.objects.filter(coachinggroups__in=[self])
+        return len(rs)
     
 # Extension of User with rowing specific data
 @python_2_unicode_compatible