Allow showing/hiding shapes and transformations

[Zardshard]

Pete gave this idea in the comments of #2748:

"Shapes should have checkboxes too. When I'm working with multiple layers in a paint program, I like to be able to hide them individually, to get a more exact idea of what each is contributing. I found I wanted to do the same with shapes in Icon-O-Matic. This is possible by unchecking the associated paths, but that's rather less convenient than a simple checkbox on the shape."

Also, it would be nice to be able to toggle transformations on/off. This would be particularly useful for perspective transformations, when you want to edit the shape when its not in perspective and then view it in perspective.