Addition of FilmGrainSynthesisApp

I have been asked to include the film grain synthesis app from https://github.com/InterDigitalInc/VersatileFilmGrain into the VTM, so that we have a tool that supports both frequency-filtering and autoregressive modes of the FGC SEI message. File headers (copyright) have been aligned with VTM ones.

It is a fully independent app, written in C (not C++) and has no dependencies with other parts of the VTM. It takes an input YUV file, a config file (reflecting the contents of an FGC SEI message) and produces an output YUV file.