Fix Midi Import of Multi-track File and CC Automation

[regulus79]

Currently, importing midi files containing multiple tracks is not supported. All of the notes get merged onto a single track.

Except, LMMS actually does support multi-track midi import, it just ignores the track index when placing the notes, and simply puts them in tracks based on their midi channel instead. LMMS does not support setting the channel of an individual note, so separating the loaded midi events onto separate tracks based on their channel does make sense.

But we don't have to choose one or the other! This PR makes it so that the notes in midi files are split into different tracks based on both their midi channel and midi track. This allows midi files which contain multiple tracks to be loaded normally, and hopefully even multi-channel multi-track midi files.

Additionally, some midi files contain a wealth of information regarding midi CC automation. Currently, we only handle pitch, panning, volume, and bank automation when importing midi files, but this PR also makes it so that the knobs in the instrument track CC rack are also automated.

Before

I'm using METAL-GTX_Demo2.mid as an example. This midi files should contain several tracks for the different guitars, along with many CC knob parameter modulations for things like vibrato, etc to be handled by the SFZ player.

Currently, everything is loaded as a single track. This made things like key switches appear stacked, which made no sense, and everything sounded wrong when played on my SFZ player. There are a few automation clips for pitch, but that's about it.

After

Now all of the tracks in the midi file are loaded correctly. The key switches make sense now, and all the midi CC modulations are loaded too.

NOTE: Regarding the CC automations, some CC numbers correspond to things like panning and volume, which are real knobs in lmms. In the case that one of these CC's are automated, it creates an automation track for that specific lmms knob. Otherwise, it automates the knob in the instrument track's midi CC rack.

[messmerd]

LGTM codewise

[regulus79]

Thanks! @extern-stat on discord tested it and said it worked, so I think I might merge it.