Lots of things! Fonts added! Checkboxes tweaked!

I have added Roboto as the main font. I am currently using a local copy of
the latest version of Roboto with the remote old version as a backup. I
added a demo css file to apply styles that probably shouldn't be in the
framework. I am still not entirely done with checkboxes, but I will
continue to tweak them along the way. Next up, dark theme!

TODO: dark theme, checkbox focus events, only fire ripple on touch (not on
click), convert roboto to other formats (eot, woff, woff2?)