Convenience method for setting all sides of Plot2D padding at once

[SheepTester]

grapheme/src/core/plot2d.js

Line 22 in 1a747b7

this.padding = {top: 40, right: 40, left: 40, bottom: 40}

Maybe that could be a fancy Padding class with a setAll method or something, or maybe Plot2D could have that method, idk. It could be hyperfancy by being like CSS's padding shorthand where one argument applies to all, two arguments does vertical then horizontal, etc.