Solver: RubarBE: Add frictions export.

src/Model/Friction/Friction.py

@@ -209,6 +209,11 @@ class Friction(SQLSubModel):
 
         self._status.modified()
 
+    def contains_kp(self, kp):
+        return (
+            self._begin_kp <= kp <= self._end_kp
+        )
+
     @property
     def begin_strickler(self):
         return self._begin_strickler