New yaml-parameter: Value focus max

[hans-ekbrand]

Cap the probability of inclusion into training for a position, regardless of its q.diff.

This idea was used to create the net posted here: https://discord.com/channels/425419482568196106/539960268982059008/874663457830633542

[hans-ekbrand]

The code is working, but I haven't tested the performance properly yet.

[Tilps]

I think mathematically - this should be equivalent to increasing the slope and the min. Specifically a 0.3 max is equivalent to multiplying slope and min by 3.3. (To get very exactly equivalent also scale SKIP by 3.3 - but scaling SKIP probably isn't needed to be 'good enough equivalence'.)

[hans-ekbrand]

Good point, but it is still convenient to have this parameter, especially since SKIP is not a yaml-parameter.