Remove progress bar as all ministrial orgs are on

As we have completed the transition of all the 24 ministerial
departments we no longer need to tell people how many are
still left to join on every page.

- Remove the bar from the layout
- Remove the JavaScript which let users hide the bar
- Remove the styles for the bar
- Remove the helpers to display the number of orgs
- Remove the relevent tests for the bar and helpers
- Moved the total ministerial department count helper into home
  controller and set it as a instance variable so its obvious that it is
  only used for home actions, updated the relevent views to use it
Remove nav helper include as the file has been removed
Merge pull request #502 from alphagov/remove-progress-bar

Remove progress bar as all ministerial orgs are on
https://www.pivotaltracker.com/story/show/48464711