[Task] Addon: Complete

[bsmithcompsci]

• Should be able to create several subscribers and publishers for various channels.
• Exposed API from C++ to GDScript.
• Exposed API from C++ to .NET. ( Stretch ).
• PacketPeer be used for the basic API communication layer.
• MultiplayerPeerExtension be used for a general API communication layer, which should use the basic API communication layer internally.
• Knowledge of Ownership.