[MusicXML] support capo element
S5 - Suggestion
The current MusicXML importer ignores the "capo" element. If a capo is used, this results in an inconsistent behaviour as the specified pitch does not match the pitch calculated from string and fret.
E.g. Recordare's BrookeWestSample.xml suffers from this issue.
Proposed solution: exporting the play transposition as capo to MusicXML and vice versa.