Document and sync parameters for each model

[pmhalvor]

My models make use of unspecified **kwargs and a self.find() function for flexibility.

However, params used in mulitple places in same model, init_components() and forward(), could possible have different defaults.

In the doc-strings for each model, specify which parameters the model uses, i.e. that can be defined in configs. Also, sync defaults across all methods within that class.

Checklist:

• doc string explain parameter w/ default
• sync defaults between all methods
• double check params in inherited methods (i.e. BertHead, IMN, evt. children of FgFlex)