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
Merge pull request #17 from alphagov/list-data-sets

List data sets
Merge pull request #18 from alphagov/allow-local-development-config

Allow local changes to development config
Add redis session support

Implementation taken from here - http://flask.pocoo.org/snippets/75/
Reauth controller

Reauth controller is triggered by a push from sign-on-o-tron. After
validating the request, all sessions associated with a user are deleted.