Add two number widgets showing the number of orgs transitioned or done

- This data comes from a spreadsheet which is a very basic clone of
  (at present) the main transition spreadsheet, containing those two
  numbers.
Use the same colours as the transition app for pre-/post-transition

Thanks to @paulhayes for CSS help.
Merge pull request #1 from alphagov/org_transition_status

Transition status widgets for the dashboard