Session support via REDIS

My attempt at adding session support to rendr-app-template. It should work even if there is no redis-server running. I hope this can be useful :-)

cf https://github.com/airbnb/rendr/issues/18

Some questions for @spikebrehm ...
 * how would one add a Handlebars view helper to say, format a timestamp? I was able to add it to the server-side but failed to get it to also work on client.
 * what's the IRC channel where I can ask stupid questions anonymously?

Cheers,
--
/a