Change colors and font.

- We now use Avenir Next as our primary font.
- Changed the colors of most things.
- Added an "accepted" post header.
- The voting buttons need quite a bit of tweaking.

Signed-off-by: Aron Cedercrantz <aron@cedercrantz.se>
Add accepted tick to question view mockup.

Signed-off-by: Aron Cedercrantz <aron@cedercrantz.se>