Make all objects stackable + improvements

A lot of objects is missing this possibility. Corner bookcases, pillars, firewood would make a perfect sense from the top of my head. But in the end all should be stackable. And stacking objects on one another shoudle be somehow adjustable. Right now you cannot adjust the level of the stacked object with the object you stack it on perfectly. Also if you make the object too big, you cannot place any other objects on it anymore. This should also be improved.