SL: Propagate profile SL to point and fix SL id cnt.

src/Model/Geometry/Point.py

@@ -15,10 +15,16 @@ class Point(object):
 
     @property
     def sl(self):
+        if self._sl is None:
+            return self._profile.sl
+
         return self._sl
 
     @sl.setter
     def sl(self, sl):
+        if sl == self._profile.sl:
+            self._sl = None
+
         self._sl = sl
 
     @property