Improve scoring system

There have been multiple complaints about the scoring system.
Currently, the score is calculated in terms of the _time_ that it took the user to guess it, rather than based on who came first.
The score of the currently drawing player is currently based on the time the slowest player took to guess it, which is also not optimal.
A better solution would be to score the drawing player based on the average speed of the players.

Optimally, we should rate the drawing player also based on how _different_ the times of the other players are, such as to encourage interesting drawings (which some players will solve quickly, others very slowly) rather than the obvious image.

No file, test, or entry point is identified in the issue. First locate the scoring-system implementation and existing scoring tests, then clarify the ranking and drawing-player formulas with maintainers. Done means an agreed scoring design is implemented and verified for different guess orders, average speeds, and time variation.

Written by the indexing model from the issue text.