Add redis session support

Implementation taken from here - http://flask.pocoo.org/snippets/75/
Remove flashed messages from index

Flashed messages are in the base template
Redirect root URL when logged in
Allow local changes to development config
Update the README to be a bit tidier
WIP: reauth controller

Reauth controller can make request to signonotron to verify user has
permissions to reauth. But then there is no way to find which sessions
need flushing from redis.
WIP - implementation actually working

Obviously needs massive cleanup and maybe some opportunities to add
tests