Start of the applicable statements for Tenancy

This is just the start of the ticket:
https://www.pivotaltracker.com/story/show/75880916

Somebody needs to pick it up and complete the rest.
Added validation for single tenancy agreement

The logic is that if there is a one tenancy agreement, one applicable
option has to be picked.
Applicable statement tests for multiple tenancies
Got it working for multiple tenancies

It needs cleanup for the rest of the changes
Horror - mess in progress, read below

This was too painful to deal with, passing it over to Stephen to take
over.
remove debugging messages
Changes to user journeys to cope with new tenancy check boxes
removed commented out lines
changed validation message + minor refactoring
renamed upto_1997_option to confirmed_first_rules_period_applicable_statements and from_1997_option to confirmed_second_rules_period_applicable_statements
only show validation error for relevant applicable statements checkbox
fixed validation error sequence
link to top of applicable statements section from validation error; make sure focus moves to correct checkbox
checkbox error styling layout changes
fix order of error messages, first order by section, then order within section
validate presence of tenancy agreement notification fields when user has confirmed first rules period applicable statements
better styling on errors
updated specs
extracted link reference logic to helper method
put error message above checkboxes