Simpler headers on mobile devices

- Substantially improve mobile device usability by vastly simplifying
headers

Known issues:
- Tablets still use the large desktop headers because they're prettier;
on tablets, the left hand side of the first letter of each line is cut
off, but the text remains readable
- On very small screens (less than about 500px), the partially navbar
covers the header; this is still a vast improvement on the previous
state