FR: coaching mode for feedback on each move

[aspiers]

It would be great if the app could offer feedback on each move, e.g.

• "Blunder" - at least 2 points worse than the best move available
• "Mistake" - at least 0.9 points worse than the best move available
• "Inaccuracy" - at least 0.3 points worse than the best move available
• "Good move" - better than an inaccuracy but still not the best move available
• "Best move!" when an optimal move was found

These boundaries were taken from https://support.chess.com/customer/en/portal/articles/1444907-in-the-computer-analysis-what-s-the-difference-between-inaccuracy-mistake-and-blunder-?b_id=12321

See also how chess.com offers analysis when you go to something like https://www.chess.com/analysis?diagram_id=647056 and click the "Run report" button (choose "Basic Analysis" to continue). See also how the chess.com UI displays the quality of each move as arrows or symbols on the chess board.

More sophisticated analysis is also possible, e.g. "2 moves slower than the fastest mate".

There could be an option to decide whether this feedback is displayed immediately while trying the puzzle for the first time, or whether it only appears later during review.

[supertorpe]

That would introduce an important impact (especially in stockfish mode), since it would force the engine to calculate not only the movement of the opponent, but that of the user. For now I leave it in quarantine. However, by solving issues #14 and #16, that is, showing the optimal number of moves vs. the number of moves made, can serve as an indicator of player performance.