Update other orgs group title to match whitehall

Whitehall is using 'Other departments & public bodies' rather than
'Others'
Do organisation sorting once only

Rather than sorting once in #ministerial_departments and once
in #other_organisations, start with a pre-sorted list for both of them.
Add a closed organisations group for departments

Also pull out the option rendering code into a partial
Merge pull request #509 from alphagov/add-closed-orgs-group-to-organisation-filter

Add closed orgs group to organisation filter