ArtemisNebula broken off from ArtemisGenericObject

ArtemisNebula and NebulaUpdatePacket broken off from
ArtemisGenericObject and GenericObjectUpdatePacket
Fixed EngPlayerUpdatePacket issues

Fixed misplaced byte field read that made it read heat values
incorrectly
Fix for EngSetEnergyPacket

Incorrect subtype fixed, replaced some hard-coded 300 values with a
constant
Vessel.getFaction() convenience method
Fixed write problem with BeamFiredPacket