BeatMaker 2 minor update

Not a massive one for BeatMaker 2, but a few notable things:

• Fix a bug where the polyphony was not correctly reloaded
• Add background mode as an option (Settings)
• Fix audio export offset when MIDI OUT was active
• Improve tempo handling while receiving MIDI clocks
• Fix pads in auto-loop when loading a preset or project
• Fix sustain pedal behavior with volume and filter envelopes