How to handle untyped learner params

[florianfendt]

Currently we have a textInput() for UntypedLearnerParams. However, they are passed down to makeLearner() as characters, so right now they only work if the param value is actually of type character.

[florianfendt]

Closing here after talk with Bernd.
There's no way to implement it other than hardcode it for every learner (well, at least for the ones
where we know the settable values)