Add workflow for grade recognition

[IonMich]

If your feature request related to a problem, please describe.
Some users might prefer to use the app after grading by hand, purely to upload efficiently submissions to Canvas. Currently one needs to retype the grade for each submission in the app. Setting the scroll height for each question can speed this up, but one still has to do repetitive work.

Describe the feature you'd like to be implemented
It would be nice if the app was able to automatically recognize the handwritten grade as a number.

Unfortunately I don't think it is possible to get a completely trustworthy identification of a single digit. The current best benchmarks for a single digit recognition under ideal conditions (MNIST) are ~99.8%. Even with a 99.8% accuracy, this could lead to a mistake multiple times per semester. Of course in a real world scenario the digit is not cleaned, so this accuracy will never be attainable in practice. In the case of university IDs, we are reaching sufficiently high probabilities because there we are dealing with fixed-length arrays of i.i.d. digits.

However, it should be possible to get a much more confident identification by writing the grade as filled circle in an array of empty circles, each denoting a possible grade. This would also allow a decimal grade.

Thanks everyone who has requested this particular feature. Feel free to expand in this thread if you have additional relevant comments.