add list of booking lines on scheduled bookings

cashbook.py

@@ -18,3 +18,13 @@ class Cashbook(metaclass=PoolMeta):
         states={'invisible': ~Bool(Eval('btype'))})
 
 # end Cashbook
+
+
+class CashbookLine(metaclass=PoolMeta):
+    __name__ = 'cashbook.line'
+
+    planners = fields.Many2Many(
+        string='Scheduled Bookings', relation_name='cashbook.planner_rel',
+        origin='line', target='planner')
+
+# end CashbookLine