Migrate frame passing to libProcessingGraph

The current solution for passing frames in the library was enough for simple processing pipelines, but it's unnecessarily complicated to implement something like adding some contrast to a video or mixing two audio tracks together. Therefore, I wrote a small library to simplify this process: libpgraph As any further change in other branches will result in merge conflicts, which would be pretty hard to solve, other branches have to be merged into main first. That implies, every issue currently in work has to be finished or brought to a working state where it is acceptable to be merged into main.