Pads should glow in a more sophisticated way

[izzyreal]

Pads glow for various reasons, and in the current implementation those reasons are a bit of a jumble.

Probably we could let pads glow in different colors for different cases, for example:

1. Pad glows blue when the user hits it via keyboard, mouse or MIDI controller.
2. Pad glows orange if a note is associated with it and that note is playing.
3. Pad glows yellow if a note is associated with that pad but in a different bank than is currently active. For example bank A is active, but pad B/01 is playing. Pad 1 then lights up yellow.

Some interesting things that should be taken into account:

1. 16 levels mode
2. Banks