Refactored styling

- [x] Switches heading font fallback to open sans, looks loads better, and is a closer font size to awkward freight sans
- [x] Switches to ems, fuck rems and px fallback
- [x] Removes any confused `display: inline-block` & `float: left/right` combos, these are not interoperable, if it's floated, it's a block, display is ignored.
- [x] Simplifies header and improves vertical alignment of text
- [x] Decreases site width a little, and adjusts breakpoints
- [x] Decreases heading sizes marginally
- [x] Decreases body text to 16px
- [x] Adjusts margins around hero and lead
- [ ] Header wraps just after the first breakpoint, needs fixing
- [ ] Fucks up the footer a bit, needs fixing

I think this is a step in the right direction, but still needs more work.

@liamjay :eyes:

Closes #25