New features of MegaDrum

A lot of things has changed. I added support for
rotary encoders as an alternative to keys. Added support for quick drum
maps switching (for live performances?). Got rid of an LCD contrast
pot, contrast is now controlled by MegaDrum itself. I switched from
DipTrace to KiCad for schematics and PCBs design. All schematics have
been updated. Some other things I don't remember right now.