Update the way how we handle Multi-Lights

Instead of having one single checkbox, which would render all lights and groups of lights in separate layers, we now have a list of all lights from where users can select which one they want to be rendered as a separate layer. Together with this, we have added a selection where users can choose if they want to render no multi-lights at all (ignore the selection made on the list), Render all the lights as a separate layer for each aov (again ignore the selection made on the list), or use the selection he has done on the list, where he can also choose if he wants to render a specific light as a separate layer for all AOVs or RGBA only.