Make calculator method to access the selected tax year
Add an error message when the select tax year doesn't contain a child
Add model spec for validation on tax year having children
Only raise an error on the child date, not tax year
Copy changes to the child benefit form fields
Fix whitespace
Copy changes to the results text when tax is due
Wrap content in an <article> tag

This makes the callout box styling work properly
Fix feature spec copy assertions
Add link to tax charge guide in conditional copy
Be valid where some children are inside the tax year
Fix trailing spaces in spec
Show alternative message when no children after 7th Jan 2013
Remove checks for nil values in child array

Whilst there might be a StartingChild with a nil start_date or
end_date, we aren't expecting any nil values present in the
array.
Merge remote-tracking branch 'origin/validate-tax-year-has-children'
Extract 7 Jan 2013 into a new contstant TAX_COMMENCEMENT_DATE
Merge remote-tracking branch 'origin/moar-copy-changes'

Conflicts:
	app/models/child_benefit_tax_calculator.rb