Small update for AI fixes

This is a small update that fixes a bug with Easy, Normal and Hard AIs not building defenses. We have also taken the opportunity to tweak the campaign. The Funnelweb mission has been reworked, to better fit the reworked Funnelweb, and the Pheonix mission is a little easier. Finally, a few crashes have been fixed as part of the push to modernise our use of shaders.