World Realm management Improvements

+ Mud.Core.Game.Game
+ -- Game.Initialzie(IDataContext, IServer) now invokes Server.Start()
if the server parameter is not null.

+ Mud.Model.Environment.World
+ -- Fixed typo'd identifier parameter for World.Remove(int)
+ -- World.Add now properly replaces an existing Realm if the overwrite
parameter is true.
+ -- World.Remove(IRealm) implemented.
+ -- World.Remove(int) implemented.
+-- World.Clear() implemented.
+ -- World.Insert(IRealm, int) implemented.