Added feature covering organisations index

and removed now-redundant functional tests.
Visualise transition state for agencies & pub bodies

Also:
• Returns groups as instances of itself.
• Implements various counts.
• transition_state_visualisation partial makes use of it.
Showing metadata for transitioning orgs on index
Merge pull request #1001 from alphagov/show-status-on-org-index

Visualise transition state for agencies & pub bodies

https://www.pivotaltracker.com/story/show/59480970