… Calling OMP_MP_NUM_PROCESSORS less often, since it's quite expensive according to profiling. Adjusting Timeline final_cache to match the video caching thread max_frames, so one doesn't clobber the other. Also, fixing an issue with openshot-player, where a video file with no audio skips horribly.

…4. Trying to experiment and reduce stuttering.

… on the Timeline and FFmpeg-related classes). The logic behind this decision, was based on profiling libopenshot and the amount of wasted CPU idle time on all the various threads. The slow code is still synchronous, and all the threads must wait on each other, adding additional overhead. So, removing lots of unneeded threads, and simplifying the underlying Timeline->Clip->FFmpegReader flow. Also, removed 2 calls to QPainter::drawImage, by improving the flexibility of Clip->GetFrame.

…t add any performance (in my tests)