New economy mode

Each tiberium crystal gives a total of $1500 or $2000 w/ enhanced
refining.

This number is then divided by the number of players on the team.
To switch back to the old mode, set aow_economy_mode to 1.

Bonuses have also been lowered to the following:

Harvester: $10
Harvester w/ enhanced refining: $20
Adv. Harvester: $25
Adv. Harvester w/ enhanced refining: $50

These values are configurable:
aow_harvesterbonus
aow_enharvesterbonus
aow_harvesterbonusadv
aow_enharvesterbonusadv

Also, fixed a few grammar mistakes on the messages for refining
tiberium.