Add ability to remap 'computer keyboard piano' keys

[tkna]

This is my own simple take on how to implement that type of request. I hope you find it helpful.

[API request] Modalization of Keybind

Summary This API allows Renoise to operate at the speed of thought. While keyboard-centric operation is convenient in Renoise, the current challenge is that key bindings are quickly depleted due to assignments to numerous functions. I believe this can be resolved by enabling the modalization of key bindings. A specific method would be something like the following: (This is merely one example as a simple idea; if there is a better implementation method, that would be preferable.) “Temporari…