-Implemented start of packet override system

-Added BatteryBlockNetworkManager
-Fixed bug with door state not saving
-Implemented main functionality for landing gear
-Implemented main functionality for solar panels
-Added CenterOfMass property to BaseEntity

-Finished implementation of network packet handler override system
-More work on the packet override system

-Added packet overrides to CockpitEntity and CubeGridEntity
-Finished implementation of battery power level packet handler

-Added GameEntityManager for tracking all entities via entity ID in the API and in-game entities
-Added CharacterEntityNetworkManager

-Added SmallGatlingGunEntity
Merge branch 'master'