generating unique names for new tracks

[szeli1]

This Pull request adds 2 methods that assigns numbers to tracks that would have the same name otherwise.

Tracks with the same name are still possible, but all new tracks and all cloned tracks will have a unique name by default. Instruments of the same kind will also have differentiating numbers added to them.

Tracks loaded from a save should not be effected.

Issues:

• Tracks that have names consisting only from digits will get the absolute highest number across all tracks. (if 1. track is named "12" and 2. track is named "automation 42", and if the 1. Track is cloned, then the new name will be "43" instead of "13")
• Change how PatternTrack clones are named #7550 does the same thing, but only in pattern track

[JohannesLorenz]

Does this close an existing issue?

[szeli1]

Does this close an existing issue?

I believe there is no open issue about this on github.