allauth: Add django-allauth.
allauth: Use allauth to logout
allauth: Sign out on GET by default
allauth: Use allauth for registration and login page

NOTE: The new functionality does not implement legal pages on
registration, however it did not work properly before either...

NOTE 2: Interface Language is dropped. See bug #3179
allauth: Add LOGIN_REDIRECT_URL to root by default
allauth: Use allauth for password change form
allauth: Use allauth for password reset
allauth: Remove duplicate error from login page
allauth: Use allauth for email confirmation
allauth: Use allauth for closed signups
allauth: Move the last template to account/
allauth: Remove now-unused EMAIL_SEND_HTML setting

The setting was used in our own fork of django-registration exclusively.
allauth supports html emails either way, so we don't need this anymore
allauth: Use allauth setting for email confirmation expiry
allauth: Drop now-unused password reset urls
allauth: Move pootle_profile urls to /profiles/
allauth: Use accounts/ as the base url for allauth
allauth: Drop registration app
allauth: Update requirements
XLIFF files can have multiple extensions

Add support for xliff extension in xliff files.
requirements: make min and pinned proper release time files

These are no longer stored in the repo and are to be built at release
time.  So no longer any confusion about changing these files during
normal development.

Hopefully this opens up some more testing against current and latest for
us.