consistent spacing scale.

[Jascha-Sundaresan]

for the purposes of consistency I propose a 2px, powers-of-two grid for keeping all nested components aligned nicely

theme.spacing: [0, 2, 4, 8, 16, 32, 64]

this will come in especially handy when refactoring the layout components

[Jascha-Sundaresan]

after speaking w/ linnutee and seeing our current design specs, I modify my proposal to:

[0, 5, 10, 15, 20, 40, 60]