Force users to be recently authenticated to view their Profile [#MEM-403]

With this commit, the user must have a recently dropped  (last 20 minutes)
SC_GA_LA ('Last Authnetication') cookie to access these urls:

https://profile.theguardian.com/account/edit
https://profile.theguardian.com/public/edit
https://profile.theguardian.com/membership/edit

Note that the UX is basic here, because the user gets booted to the normal
sign-in page (even tho' they're already signed in):

https://profile.theguardian.com/signin?returnUrl=https%3A%2F%2Fprofile.theguardian.com%2Faccount%2Fedit

https://jira.gutools.co.uk/browse/MEM-403