[WIP] Convert all chunk-related logic to the new system's semantics

Replaced all references to chunk->players and chunk->NPCs with
chunk->entities and all instances of the old NPCClass enum with
EntityType.

The server compiles but will not yet run properly.

src/core/Defines.hpp

@@ -24,14 +24,6 @@ enum eCN_GM_TeleportType {
 	eCN_GM_TeleportMapType__Unstick
 };
 
-// NPC classes
-enum NPCClass {
-    NPC_BASE = 0,
-    NPC_MOB = 1,
-    NPC_BUS = 2,
-    NPC_EGG = 3
-};
-
 // nano powers
 enum {
     EST_NONE = 0,