Reimplemented the push/pop entity methods in RoomManager

Some accessors in Entity had to be made const, as they were being called
from lambdas with const parameters.

server/rooms/room_manager.hpp

@@ -22,6 +22,7 @@
 #ifndef ROOMMANAGER_HPP_
 #define ROOMMANAGER_HPP_
 
+#include "entity.hpp"
 #include "room_data.hpp"
 #include "singleton.hpp"
 
@@ -42,6 +43,9 @@ public:
 	void UnloadAll();
 	void UnloadIf(std::function<bool(std::pair<const int, RoomData const&>)> fn);
 
+	void PushEntity(Entity* entity);
+	void PopEntity(Entity const* entity);
+
 	//accessors and mutators
 	RoomData* Get(int uid);
 	RoomData* Get(std::string name);