Move loadScheme to AST.Term.Scheme
Other parts belong to the upcoming nominal terms

This let's more easily read the actual interesting code :)
Note that there's more than 60 lines ...

Oops!
The two instances of Instantiate weren't really the same thing!
One was used for let-gener...

Towards adding content :)

And more re-use potential when different term types have same constraints

It doesn't offer a lot of value and doesn't work for all cases anyhow

and renames in Row

Before this change a non-top-level occurs error would had slipped the check

Manual instances will have less code to write

This reverts commit ba80bd86e49b53380f5397ba08400...

(not necessarily a change for the better but doesnt trigger hints)

Allows to store a serializable scope

Infinite term is now quantified to a variable for both error reporting,
and possibility of langu...