Implement Correlated Multi-Jittered Sampling

[oktomus]

Sorry for the new PR, it was getting really dirty #1937

Paper

Testing it

1. In the appleseed fork directory, get the last state of master.

git checkout master # If not already
git pull appleseed_remote master

2. Run cmake and compile, this will be the build using Halton sampling.
3. cp -r `the whole fork directory somewhere
4. Get the CMJ code

git remote add oktomus [email protected]:oktomus/appleseed.git
git pull oktomus cmj
git checkout cmj

`5. Run cmake and compile, this will be the build using CMJ sampling.

What still needs to be done

1. Compare convergence rates of QMC and CMJ

Next ?

Implement a progressive mode using CMJ https://graphics.pixar.com/library/ProgressiveMultiJitteredSampling/

[oktomus]

Thanks for the review @fedormatantsev and @dictoon :) I commented some of your remarks.