Item System

So far it's just the basic skeleton of "items" which I tried to model how you did with other pieces of code. For now I've created an ItemSystem which contains a map of BaseItem* and initialized a bunch of example items in ItemSystem::init();

`````cpp
BaseItem * b = new BaseItem();
b->setName("sword");
b->setValue(20);
`````

I don't know what properties every item should have and etc etc.