Update fretboard to current position on playback

[MLK97]

I don't know if this has already been considered but I think this could be a nice feature. I could take a look at it if you want.

[dmitrio95]

That pull request was actually needed to improve handling of note input cursor in plugins, and it is not related to the playback position which is handled in MuseScore completely independently from the note input state. Currently MuseScore plugins cannot retrieve the current playback position, so more changes to the plugin API are needed to make it possible to implement this feature.