Summoned mobs are now actually treated as mobs.

Unfortunetly, this necessitated keeping around yet more JSON objects for
the duration of the server's runtime.
It also involved unifying the way NPC IDs are handled, such that they
may be allocated and deallocated out of order.

If any NPCID-related bugs occour, this commit should be regarded as
the prime suspect.

src/NPCManager.hpp

@@ -4,6 +4,8 @@
 #include "PlayerManager.hpp"
 #include "NPC.hpp"
 
+#include "contrib/JSON.hpp"
+
 #include <map>
 #include <vector>
 
@@ -18,6 +20,8 @@ namespace NPCManager {
     extern std::map<int32_t, BaseNPC*> NPCs;
     extern std::map<int32_t, WarpLocation> Warps;
     extern std::vector<WarpLocation> RespawnPoints;
+    extern nlohmann::json NPCData;
+    extern int32_t nextId;
     void init();
 
     void addNPC(std::vector<Chunk*> viewableChunks, int32_t);