White to dark theme on page loads

[ryanrampage1]

Chrome Mac: When a page loads it flashes white then flashes to the dark theme.

[mhammerly]

the theme preference is stored in a cookie, we can probably make rails serve a different stylesheet depending on the setting instead of applying the dark theme with async javascript because this is known serverside

[mhammerly]

fixing this would enable #50 to go away cleanly too