Auto switch between HTTP and HTML redirects

[jace]

Flask-Lastuser recently switched from HTTP to HTML redirects (HTTP 301 to HTML Meta: Refresh) to ensure logout worked properly for Eventframe. This was needed because HTTP redirects pass through the original HTTP_REFERER header, which may be the event website, which Lastuser isn't aware of. However, HTML redirects render the interim page to the user, which is distracting.

Flask-Lastuser should examine the current HTTP Referrer header and make a call on which form of redirect to use.