Added copying of cell's layer properties to the draggable view

Hi, 

I had a small problem with cells which had nonzero corner radius and shadow as well as some scale transform (e.g. on selected cells). The properties were not copied to the draggable preview image view and it looked strange.

I've added a simple fix which copies main layer attributes from the cell view to the draggable preview and also calculates the preview frame based on the bounds property (and adjusts the center) which works even when the original cell has some scale transform.

Cheers,
Bartosz