Hitbox fixes combined with some shield changes

This PR is to discuss/review the code, any changes will be made on this fix-hitboxes branch at FAForever/fa.
OK so these were necessary because all the T3 Air and Naval Factories have 120 BuildPower vs 90 on the Land Factories. In order to have all three types of factory build Engineers at the same rate as each other, this modifies the BuildPower dynamically when production starts, if it's an Engineer on the platter.