Render layer management

[riggles]

It would be helpful if we could manage render layers a bit better. Currently, the layers are only numbered, and there's no indication of how many are actually used in a scene. So if I had to go back to a shot and re-render a layer, the only way to know which one it is, is to cycle through them.

Being able to name the render layers uniquely and so they can be selected from a list would be much more production friendly, as well as using that name in the filename output of a rendered image/sequence.

[Tutor]

Seconded.