cache the builder view based in latest strip number

since the same view is used to show all and the latest strips
the cache use also the params[:latest] as cache key.
make sure the secret key comes from environment variable
use Memcachier addon in production
add Code Climate badge to README
add Valid Atom fedd badge to README
add travis-ci build and badge
move newrelic gem to :production group
add Gemnasium badge