Add ConfirmationLink model
Add capability for one-off link for requestor status updates

As it stands, the user-supplied status will be stored but not used
by foi-register and will be sent to WDTK as the definitive outcome
status

Dummy copy in place for now
Move with_alaveteli helper to test_helper.rb
Send the user's status choice to alaveteli
Better random token generator
Add confirmation link to response email template
Send public body status changes to alaveteli
Add closed_state recognition to request
Split response mails into update and outcome templates
Remove holding text for response update confirmation page
Merge branch 'issues/169-ask-user-to-confirm-request-state'