Added msg to ask users to add pvb email to their address book
Convert confirmation page content into Markdown
Add conditional_text helper for Markdown content
Merge pull request #49 from ministryofjustice/addaddressbook_LM

Added message about adding PVB email to address book on confirmation page and email
Added another misspelt domain to the blacklist.
"secret links" are now shorter.
MetricsLogger is fault-tolerant.