CSS overhaul, and pulse visualization

Metrognome has a lot of baggage CSS, and not thrilled about how it looks.  This fork simplifies entire index.html

Calculating bpm is great, but think it really needed to be visualized, through a pulse (implemented).  Flashing might be epileptic, but it's a demo of what else could be possible.  Perhaps next could be like a true metronome wand in the BODY's background.