Track headers

[kybos]

With reference to #729

Just experimenting, what about something like that:

Seems more visually appealing to me than the single-letter abbreviations...

[terminator356]

Yes, exactly what I meant. Looks cool. Love the track column thingy.
I think what stopped me was IIRC I was worried about certain contexts or something.
Maybe it was that mute and solo have two states, can't remember. Still, looks cool.