A small suggestion regarding undo/redo

The action of toggling layers to be visible/invisible should not be added to the undo/redo queue. Reason is as following
When a layer is invisible and the user accidentally draw something, they usually don't notice at first. Upon making the layer visible, the user will realized the mistake and naturally go for an undo. However, since the action of toggling the layer is included in the undo Queue, the layer become invisible again once the user hits ctrl-z, making it very difficult to know when to stop hitting the button to return the sprites to the previous state