Update to Rhythm Lab v1.1

Thanks to everyone who tried the initial release. This first update is pretty minor, with the following changes: 

• Added twenty "demo" samples to the sound pool. 
• Added a button to "Remove Demo samples" from the sound pool. 
• Fixed an issue with the "Filter Cutoff" slider causing distortion.
• Made some changes to formatting & button placement.

Any suggestions are welcome in the comments. I want to make this a really useful tool for anyone making electronic music. 

Cheers!