use locale rules for the challenge hashes

restore old land hashes which in theory should not have changed in .24

Separate synced pixels from land digests - this is mostly to allow the official racer digests to remain unchanged.

Merge nemo's hash change commit

Add exit hint after Basic Movement Training

Easier back jumps in Basic Movement Training (fixes bug #692) The explanation of Back Jumping (2/2) has been simplified and the "hard" part has been made easier by lowering the girders. The original idea was that I wanted to force players to learn how to jump higher by delaying the 2nd backspace keypress. But this turned out that this section was too unfair and we have lost at least one player due to rage-quitting, according to feedback.