Build 080721

Basically the logical outcome of the previous build (I accidentially dropped), (hopefully) fully de-glitched.

• The missing controls now work correctly, added a few more (like zoom etc).
• DI stack. Like before, see "HELP DI" for details, tho basically now many commands (starting with "DI INIT") support a slot ID from 0 through 3. What happens is you now build a control stack, where device #0 is the base one, and #1 extends/overrides one's inputs, next go #2 and 3 (any can be skipped, so #1 and #3 alone is perfectly valid). The stack is fully dynamic, and unplugging a controller causes a fallback, restoring the previous one's inputs it used to override. The logic allows to create a layout featuring a set of inputs with multiple sticks, pedals or switch pads.