Adds dice-twenty-card component

Makes a demo card to get a random dice roll.

![selfie-2](http://i.imgur.com/nXAmeH7.gif)

The dice-twenty-card component allows you to create extra text above
the dice and also adds a button to roll the dice.

I also spent (too much) time tweaking the CSS so it appears correctly
in the Cordova app and also in the Chrome preview.