Feature Request: Math Operators for the GUI Input Fields
### Math Operations
The ability to have math operations in the *stack layers* and *padding* fields similar to other input fields in Sketch (addition, subtraction, multiplication, and division). I figured this would be helpful as a tiny quality of life feature. I often space or pad things consistently by multiples of a certain number, I know it's an arbitrary and possibly an unusual practice but it's lead to really great consistent results for me!