[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/Player.hpp

@@ -93,6 +93,8 @@ struct Player : public Entity {
     time_t lastShot;
     std::vector<sItemBase> buyback;
 
+    Player() { type = EntityType::PLAYER; }
+
     virtual void enterIntoViewOf(CNSocket *sock) override;
     virtual void disappearFromViewOf(CNSocket *sock) override;
 };