Bold for page titles

first step adding bold to the site - adding it to page headings and the
big numbers on homepage and 'how gov works'
Add bold and tidy up some spacing around the site
New styles for contact details

- move keylines about
- adjusting typography
- dicking around with whitespace
Remove redundant selector

Couldn't find anywhere this selector would actually do anything. Check
org pages, topical event pages, world location pages etc.
Remove comments and use media mixins
Merge pull request #282 from alphagov/add-bold

Add bold

https://www.pivotaltracker.com/story/show/43437867