Improve MIDI control and key binding to reset track head position.

[fnky]

Is your feature request related to a problem? Please describe.

There are a few things that I think could be improved to make the experience a little better:

• If you want to stop playback and reset track head position, you have to use your mouse to press on the "Stop" button.
• MIDI notes keep playing when pausing/stopping while one or more notes are playing. This is especially tedious if you use synths with sustain, as they will keep on playing until you resume to the end of notes.
• Cannot disable volume MIDI control. It blasted my ears because the volume was set to 100% in the sequencer, but expected it to be at 50%, as I had set in my synth — the MIDI control overrode my synth's volume control.

Describe the solution you'd like

• Allow ENTER key to stop the playback and put the track head back to start position.
• Stop all notes on pause/stop — currently a note keeps playing when you pause or stop while notes were playing.
• Have a setting to disable other MIDI controls like volume, and only listen for MIDI notes.

Describe alternatives you've considered

I don't believe there are other alternatives.