shared_ptr -> std::shared_ptr

This is one of the first commits in a plan to remove all `using namespace std;` lines in the entire codebase as it is considered anti-pattern today.

Minecraft.World/BossMobPart.h

@@ -23,5 +23,5 @@ protected:
 public:
 	virtual bool isPickable();
 	virtual bool hurt(DamageSource *source, int damage);
-	virtual bool is(shared_ptr<Entity> other);
+	virtual bool is(std::shared_ptr<Entity> other);
 };