Fix bank parameter for music export

[borbware]

This commit fixes the bank parameter for exporting music (see issue #2190).

There is still some ambiguity present, because the exported music depends on the sfx bank as well.

If bank chaining is on, the exported music uses the same sfx bank as the music bank.
If bank chaining is off, the exported music uses the sfx from the currently active sfx bank.

This could be fixed by introducing a chained=true/false parameter for the export.

[borbware]

Note: I didn't manage to call the static switchBank function, so I implemented some of its functionality inside studioExportMusic.