Column opening/closing_on replaced with x/x_at date time attrs.

• Renames attributes closing_on to closing_at, and opening_on to opening_at
• Modifies date select in admin to include time
• Front-end now displays time in ordinal_long format
• Expiring consultation cache when they open / close
• Consultation scopes compare to Time.zone.now instead of Date.today
• Renames Consultation validation to validate_closes_after_opens
• Adds tests for PublicationesquePresenter#time_until_closure and changes it to handle times
• Modifies some other tests involving consultations to use times
Moved admin-only helpers into admin side

ConsultationsHelper#consultation_opening_phrase and consultation_closing_phrase were only being used in the admin suite.
They are now included in an admin helper.

Also updated the language to be 'Opens at' instead of 'Opens on'