#18 EcoAccount funding

* adds constraint for setting the deductable_surface too low -> existing deductions would not be valid anymore
* adds/updates translations

compensation/models.py

@@ -298,6 +298,14 @@ class EcoAccount(AbstractCompensation):
         if self.deductable_surface > after_state_sum:
             raise ValidationError(_("Deductable surface can not be larger than existing surfaces in after states"))
 
+        # Deductable surface can not be lower than amount of already deducted surfaces
+        # User needs to contact deducting user in case of further problems
+        deducted_sum = self.get_deductions_surface()
+        if self.deductable_surface < deducted_sum:
+            raise ValidationError(
+                _("Deductable surface can not be smaller than the sum of already existing deductions. Please contact the responsible users for the deductions!")
+            )
+
     def save(self, *args, **kwargs):
         if self.identifier is None or len(self.identifier) == 0:
             # Create new identifier