Speed up the 2-step flow

[r002]

From yobi9's Discord comment on 3/10/21:

Speed up the 2-step flow: the verify mode right now helps verify that the capture and OCR is correct, before doing final render in step 2. Both steps do the OCR from scratch however, so it's a little slow. In tetris_rate_adder, I also add a verification step, but that step would dump all the OCRed data to a json file, which could be used to process the final output in step 2 without having to do the OCR again. That was much faster. I dunno why I didn't do it this time :thinking: