Keyboard bindings

[ericyd]

• Add "KeyboardProvider". This context exposes a simple way to bind keydown events on specific keys to a callback. A context is useful here because it allows the app to use a single callback, and delegate the event based on which key is pressed.
• Bind keyboard to following events
  • space (play/pause)
  • c for muting the click track
  • 0-9 for selecting a track
  • r for arming recording on a specific track
  • m for muting a specific track
  • i for monitoring input on a specific track