Train Designer: Add Filter Option to "Add Train Cars" Buttons

Currently, it is kind of tedious to set the filters on train cars in the train designer for very large trains since you have to set the filter individually on each car after it is added to the new train. It would be nice if the filter selection drop box was added to the "Add Train Cars" button for each wagon type, and would be used as a default filter when the car is added to the train.
This makes building large trains that carry a single product less tedious, and avoids needing to add a copy/paste system to the filter UI as an alternate solution to the issue.