(v0.6.0-dev) Added Sweet Alert to demo page and made button font-sizes relative.

Answers my Improvement #68. If you don't like it feel free to remove it again of course, but just to give an "active" demo where users can check the button functions as a regular button.

Note that we can't make the [Sweet Alert](http://tristanedwards.me/sweetalert) button use Waves without hacking the core of Sweet Alert, or adding extra stuff into style.css. Because it writes to the page after Waves instantiates means that no Waves event handlers get instantiated on the OK button. I wonder what the cleanest way to solve this is?

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Also made the font sizes, line heights and padding relative sized.