Added algorithms for EncounterManager to create enemy opponents with randomized stats.
In encounters, each  opponenet now has a randomly created ship with weapons, shields, gadgets, cargo, and random hull strength.
Added getRandomTradeGood() to trade good class. Added class Tools with a method for getting a random element from a weighted list.
Modfied values in GadgetType enum. Added contains() method to EquipmentSlots.