Feature/flip mode

Flip the content of show/reveal.
Save state.

I decided to keep track of this entirely in JS, using localStorage for the state.
I was unable to successfully find a way to write a test for this... Maybe if I separate it out into a component and use a "fixture". I'm not sure if that's overkill, or if adding phantomjs would be overkill.

@arthurian ?
I don't think this should be using an `id` here. Maybe that's why it's only flipping the first card? Every card will have the same id, so this should be a class or data attribute instead.