Refactored styling

- [x]Switches to ems, fuck rems and px fallback
- [x] Simplifies and improves vertical alignment in header
- [x] Decreases site width, 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 neds more work.

@liamjay :eyes: