PSI pieces left hanging

[luke-kiernan]

With splitting off a piece of PSI, there's parts that are left hanging. I'm opening this to record instances of such things.

Called, but not implemented here:

• get_min_max_limits (PR add stub for get_min_max_limits #3)
• get_parameter_column_refs

Implemented here, but not called anywhere:

• get_offer_curves_for_var: not called in PSI either! Seems to be a leftover from some unfinished refactor, or maybe something got lost in a merge.

[luke-kiernan]

I realized a lot of the files in the repo were verbatim copy-pasted from PSI, and weren't actually included. Will close this issue.