Do not allow gaps in tuplet, make invisible instead
In MuseScore 2, we have several problems happening because of gaps in tuplets. Gaps are created when one delete a rest in a voice > 1. It has been proposed several times to disallow the deletion of rests in tuplets and instead make the rest invisible. We could also make rest in voice invisible when the user tries to delete them.
For problems, see
* Also the fixTuplet function and https://musescore.org/en/node/136406, https://github.com/musescore/MuseScore/pull/2881