Add the ability to create music sheet pattern.

[KristijanZic]

I'd like to propose a feature request, a music sheet pattern. I'm not sure on the best way to implement this but maybe it could be done by implementing a feature in the settings called "Pattern Space" and Pattern group when the Pattern is set to Lines.

Pattern Space would create a different height between Pattern Groups and Pattern Group would be a number of lines. Pattern Height would still stay as height between the lines in a group or in a page if the Pattern Group is set to 0.

This app is totally different but I'd like to share a link to a proprietary app that the devs of rnote might wanna look into and maybe use it to get some inspiration for rnote. It's called notability: https://notability.com/

[Kreijstal]

I would like to hijack this, and simply say it would be nice if you could add backgrounds on rnote, ala xournal