[refactor] Remove the word 'Manager' from most source files/namespaces

ChatManager -> Chat
MissionManager -> Missions
NanoManager -> Nanos
TransportManager -> Transport
ChunkManager -> Chunking
BuddyManager -> Buddies
GroupManager -> Groups
RacingManager -> Racing
ItemManager -> Items

NPCManager and PlayerManager remain.

Note: You can use git log --follow src/file.cpp to trace the history of
a file from before it was renamed.

src/NPC.hpp

@@ -1,7 +1,7 @@
 #pragma once
 
 #include "CNStructs.hpp"
-#include "ChunkManager.hpp"
+#include "Chunking.hpp"
 
 class BaseNPC {
 public: