Introduce robots.txt and sitemap for docs
Remove IE specific CSS file

We've never used this anyway. It just hangs around doing nothing.
Merge branch 'master' of github.com:TryGhost/Ghost-UI

# By Fabian Becker (1) and John O'Nolan (1)
* 'master' of github.com:TryGhost/Ghost-UI:
  Remove old %extend placeholders
  Fetch bourbon/breakpoint/normalize via bower