Remove the Sine scene and rearrange groups

Checkout the tag "sine" for the neat spring animation I had going. I set
out to learn how to synthesize an audio sine wave, but came across the
fact that undamped springs oscillate in the same manner, so I made it
happen with SpriteKit.

The spring physics animation took no more than 15 minutes, but learning
audio synthesis took many hours!

In particular, this image was the influence on using a spring:

http://en.wikipedia.org/wiki/File:Simple_harmonic_oscillator.gif