Drag and drop render layers to re-order them

As much as I know, actually, you can't re-order layers on the list dropdown menu, so they appear on creation order. That, if you have many, is not the most usefull way to show them.

So main proposal is to allow re-ordering render layers. It would be nice to do it by hand or, at least, alphabetically, creation order, last used, etc ...

I see that them appears on the outliner on the scene level, if we can drag and drop to reorder would be more than helpfull.

That's it, an easy idea to ask for... probably harder to program, let's see if we catch some programmers attention.

Cheers.