Improve README
Show committer details in header

This commit uses the output of `git config` to show the committer
name and avatar in the navbar.

Improves the colour and words of the draft badge.
Add link to 'Recent config changes'
Prevent crash when Jenkins can't be reached
Show success/error flashes when saving
Merge pull request #1 from alphagov/improve-look-and-feel

Improve look and feel