Enable upload and rendering of music in MusicXML format

Although it is possible to upload PDFs for songs, these obviously do not transpose automatically as the chord charts do.
It would be great to be able to upload different instrument parts or custom songs and arrangements in the standard MusicXML format. These could be rendered and made to respect the selected transposition settings using OpenSheetMusicDisplay (https://github.com/opensheetmusicdisplay/opensheetmusicdisplay).