Tonuino with analog volume controls

A fork of https://github.com/tonuino/TonUINO/tree/All-in-One-PLUS . Main changes:

• Use analog volume control (via potentiometer) instead of buttons
• Remove all 5-button code

Useful material:

• Behind the scenes wiring: https://maker.pro/arduino/projects/how-to-use-the-dfmini-player-mp3-module-with-arduino
• Script for moving files into SD card: https://github.com/bahnfrei/tonuino-sdcard/blob/master/tonuino-sdcard