Feature Request: Stacked layers with fixed width/height?
### Feature request / enhancement

I have 4 objects that are spaced with 32px padding between them, centered in a 375 canvas. This stack is a total of 352 in width.

If I duplicate an object inside the stack, Paddy does what you would expect: Moves the object over and spaces it out with 32px padding. This increases the overall width of the stack to 424px.

What I would love is for the option to denote a fixed height/width stack, with objects inside spaced 
out evenly instead of a strict pixel amount.

I apologize if this is a duplicate request.
Thank you!

![screen shot 2018-08-30 at 12 14 55 pm](https://user-images.githubusercontent.com/4248053/44873928-66fbba80-ac4e-11e8-8741-f3a1657bde85.png)
