Update Mzalendo design

Fixes https://github.com/mysociety/pombola/issues/1359

- [ ] Remove survey header (if it's not already been removed by https://github.com/mysociety/pombola/pull/1368)
- [ ] Simpler, flatter green header
- [ ] Wide navbar, with new items
- [ ] Clean up homepage:
  - [ ] New hero image??
  - [ ] Prominent links to Search, Hansard and Rights
  - [ ] Large, centred mission statement below hero
  - [ ] Larger links to blog posts, more whitespace
  - [ ] Narrower sidebar containing tag cloud, featured person and Twitter feed
- [ ] Redesign person page:
  - [ ] More friendly 'polaroid' style profile pic
  - [ ] Less abrasive party / county links under profile pic
  - [ ] Distinct sections for Experience, Appearances, Contact Details etc.
  - [ ] Move Share / Correct / Comment buttons alongside title
  - [ ] Generally better typography
  - [ ] **Change from supercool mockups:** Put Disqus comments into their own section