Expiring User Upgrades 2.5.2

• Fix "Undefined index: sv_exup_email_on_expiring_expired_upgrade" by installing default registration settings on upgrade instead of just install.

• Actually apply user registration defaults on account creation
• Allow admins to edit user add-on email preferences
• Fix added email preferences not displaying
• Require XF 2.0.4+

• Fix "Undefined index: recurring" when reversing a user upgrade due to a chargeback

• Version bump for 2.0.0 release

• Fix sending expiring notices being sent well before the expiry timeframe (resets the notify date flag)
• Fix Extending upgrade feature, please audit any extended upgrades to check if they had been set to a non-expiry upgrade by mistake