Address findings from issue #1475

[derselbst]

This addresses the findings of issue #1475, in particular:

• Update the documentation about the load shell comand
• Revise error handling of the load shell command
• Allow drum channels to profit from Bank Offsets by no longer ignoring MSB Bank changes for drum channels (second try after allow bank changes on drum channels #176)
• Make the preset fallback logic on drum channels more predictable, to migitage my concerns in 883b640. I.e. instead of directly falling back to preset 128:0, we are now falling back to bank 128, while keeping the currently set program. And only if that fails as well, we pick the standard drum kit at 128:0.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
16.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud