Loop regions like items

[Fergler]

Would love this feature especially for EDM production in it's early stages.

Suggested implementation would be to render all the items in the looped section as gray and more translucent (like Empty Items) and not be able to click or edit them in anyway (... option? I don't think it's necessary imo, since use-case would be smaller regions that are conducive to looping and hence would probably already be on screen or right next to the current area).

As for user input method:

Currently you drag the region sides to extend or shorten it's bounds. That's fine, shift modifier for loop? Or, to be more in line with how items loop, switch them so regions loop on regular drag and change size on shift+drag. I think that's better because it's more consistent.