refactor picture buffer to allocate buffers for current frame and not for the entire GOP
Allocate PIC_TRUE_ORIGINAL and PIC_FILTERED_ORIGINAL only for the current frame instead of the entire GOP. (respectively PIC_TRUE_ORIGINAL_INPUT and and PIC_FILTERED_ORIGINAL_INPUT for RPR case) This save around 8-10% of peak memory usage for RA classA (around 1.5 GB)