Add RCL8 economic settings
Add RCL8 economic settings

Creates a new set of options that are only applies at RCL8, which
currently includes downgrading the priority of controller upgrades.

For levels below RCL8 the `EXTRA_WALLBUILDERS` is now set to
ECONOMY_BURSTING, but at RCL8 it remains at `ECONOMY_SURPLUS`.

ScreepsQuorum/screeps-quorum