- Added TimeLine, which is a scrolling panel with grid functionality,
similar to a piano roll window.

- Added MIDI functionality: now you can choose the MIDI device you want
to use from PatternCombinerUI.

- Meanwhile, MidiScheduler is broken and EventBuffer is gone. Intending
to create a system where timing is precalculated to simplify buffering.

- UI classes are greatly simplified with the various block GUI elements
factored out.

- Various refactorings.