FR: Add button to change grid to triplets to the midi editor

[don_ortalion]

Now there is a chceckbox on the controll panel, but it is inconvenient to use it because it changes position when i minimise the panel.

[spoontechnique]

Yes, I find it frustrating that the only way to work in triplets is to use the global triplet switch. I often have to go back and forth, and there's no keyboard shortcut. Similarly, the only way to work with quintuplets or other tuplets is with Step Clips, which doesn't help with audio clips.

[paulo_apo]

Ditto.

In fact, would be great to have the option to set grid freely, rather than just being bound to zoom.