Triggers have a basic response to character collision

I've hacked the trigger system to create a really basic teleport pad,
using the dirt tile as an indicator. This behaviour is not coded into the
engine, but is in fact scripted in lua.

This commit is messy, due to lack of sleep.

server/entities/entity.hpp

@@ -28,6 +28,8 @@
 //The base class for all objects in the world
 class Entity {
 public:
+	virtual void Update();
+
 	//accessors & mutators
 	int SetRoomIndex(int i);
 	Vector2 SetOrigin(Vector2 v);