Add more documentation to control object

[brandmaier]

@manuelarnold suggested (in 2021) to improve documentation in semtree control for:

Linear: Boolean. Identifies non-linear constraints. Can we derive this automatically?
strucchange.from, strucchange.to: Those are important for maxLR and maxLM.
strucchange.nrep: add more info
scaled_scores: Should probably always be TRUE and be removed from control object.