Description: Adds a shield of <sShieldType> to a ship.
Arguments: <rShipTable>: Reference to the ship; this should be NewShipType. <sShieldType>: The type of shield; only "EMP" seems available. <iMaxShield>: Max value of the shield for this ship; the value is in the same units as health and damage. <iShieldRechargeTime>: Time in seconds for the shield to go from 0 to max value.