Re-implemented the scripted bonus value functionality, to let the expansion chance be controlled via DB entry.

Stratified the expansion chance starting at a level 3 settlement (9%) to a level 5 settlement (13%).

After correcting the >= issue in a previous update, the balance was sorely affected, necessitating a system rework. The final product is noticeably weaker for AI, but should still prove useful in the hands of players.

I was using >= instead of < in a couple areas, resulting in expansion only happening if all the settlements were NOT fully upgraded.