CRM-13179 fix country autofill
CRM-13179 use api function to get billing defaults in a sharable way
CRM-13179 use api function so get billing defaults in order to use 'sensible fallback' if billing address doesn't exist
remove debug
Merge pull request #1494 from eileenmcnaughton/CRM-13275

CRM-13179 fix country autofill
Autofill via cid=N and via autocomplete working properly for event registration and online contribution pages.
There are a few edge case bugs which I will post separate Jira issues for.