Support per track volume from Guitar Pro 7 file format

[jordanske]

Description

Currently when using .gp files from Guitar Pro 7 all track volumes are the default (15).
Alphatab does not use the track volumes set in Guitar Pro 7.

This works fine with .gp5 files but fails to do so with .gp.

Setting in Guitar Pro 7:

Exported as .gp5:

Exported as .gp:

Possible Solutions

Modifying the gpif importer to support this.
I already created a pull request with a possible solution: #445

Current Workarounds

Using .gp5

[Danielku15]

Thanks for this finding and your planned contribution. Funny I never realized that the volume components are missing when read. It seems that also other parts like the balance are missing, would be good to add them too.

[Danielku15]

Closed with #445