Typography updates

* Make the container divs narrower and centered in the middle of the
  viewport
* Center heading text
* Make h2 font size 60px
* Make section paragraph font size 22 px, line height 1.5
* Use sans serif font for headers
* Use serif font for body text
* Make timeline take up the full screen width

Fixes https://github.com/sc3/cook-convictions/issues/96