Added option to scale pitch with transaction size

I've seen the suggestion thrown around on reddit, so I took the time to implement it.

There now is a checkbox to enable that option, which will make bigger transaction sound deeper. It'll scale logarithmically from 0.01 BTC to 1000 BTC, then it will cap to the deepest sound available. To prevent all small transaction from making the same, high-pitched noise, I added some fuzzing so that the sound played is ± 2 from the actual pitch corresponding to the transaction size.

Thank you for making this site! It's a nice background for me to listen to while working. =)