Fixed issue with last update removing Archeologist building prereq.

Now makes sure all building prereqs are set appropriately for units that already had a building prereq.

Fixed issue where Warrior Monk unit was included in both the Land Combat and Religious unit class limits. Now any unit which has Formation_Class_Land_Combat, but is also religious, will only be classed as Land Combat.

Removed limit on aircraft units - these units are already limited by aerodrome/airstrip space.

Added limits to settler, builder, and naturalist units, to prevent AI spam.

Increased load order, to prevent mods which edit the unit table from be incompatible.