Add Building Effect in Editor

[nedfumpkin]

I have figured out a way to change some things on the add building effect in the editor. There appears to be a maximum number of buildings that show up in the list, and with recent additions, it stopped at the Sand Pit. This meant that event effects could add the steel mill, nor the weapons factory.

I've figure out a way of changing some of the industries that appear on the list, and so I have been able to move the steel mill back on to the list by replacing the sand pit. This means that it is again possible to add a steel mill via effect, but no longer a sand pit.

So this will mean that it might be necessary to go back to maps and re-adjust any event effects that were adding any industries.

This might affect industries that are spawned, but I can't say for sure.

In any event, I think it will be worth it in the long run since the textile mill and tannery will be available to events.