Echo Pad update

Here's what's new:

• new effect: Smooth Filter (input filter)
• new random preset generator buttons create a random preset when pressed.
• The button labeled "???" generates "safer" presets with no distortion/decimation/etc. The button labeled "!@#?" allows distortion/decimation and is more unpredictable. Tap on either button until you hear something you like!
• added options to select inputs when using 2 channel USB audio interfaces: Input 1+2 (stereo, default), Input 1 or Input 2
• fixed a bug with loops that were exported from the main looper
• minor bugfixes