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. applying a fix similar to [the one used by rails](http://api.rubyonrails.org/classes/ActionView/Helpers/FormHelper.html#method-i-check_box-label-Gotcha).