Enable all services to be deselected for a WWO

www.agileplannerapp.com/boards/173808/cards/8045
fixes: https://govuk.zendesk.com/agent/tickets/802017

adding a hidden field for the check box group for
services for a worldwide organisation, which enables
deselection of all services, similar to:

http://api.rubyonrails.org/classes/ActionView/Helpers/FormHelper.html#method-i-check_box-label-Gotcha
Merge pull request #1868 from alphagov/fix-service-deselection

Enable all services to be deselected for a WWO