Internal light and mesh interface rework

[Dade]

In the past days, I have done a huge rework of LuxCore internal light and mesh interface. This start as a fix to this (https://github.com/LuxCoreRender/BlendL ... issues/310) problem and ended as a huge rework. This was done to align C++ and OpenCL results and to add full support for instanced and motion blurred area lights.
It also include a lot optimization to speed up the rendering of instanced and motion blurred meshes/light sources.

The most visible result is probably the full support for motion blur area lights. This was before (light sampled only at time = 0.0, at left):

and this with the new code (light sampled over all the time interval, from left to right):

[Racleborg]

Sorry for late response, but I've only just realised the significance of this work.
Many thanks.