Reverse trigger key (kit + slot) identifiers

[adamrenklint]

The combination of the ID assigned to a kit and a slot trigger could be called trigger, outlet, or something like this.

The shorthand representation for an oscillators frequency should definitely be called key, not note, since a note is already something else in Bap.

[adamrenklint]

Refactor to the scheme that trngl will use:

• kits have numeric ids 0 - Infinity
• patterns connect like pattern.kit(1, drumKit)
• slots are named A-Z
• call it trigger key and format like 1A