Temporary commit to generate contracts for row poly

!!! Fix this eventually with real sealing contracts
Fix init-env serialization of PolyRow
Fix minor error
Fix class type subtyping

Although classes have no non-trivial subtyping relationships,
the representation I chose ends up introducing cases where two
"equal" types are not represented in the same way. This
commit fixes that by checking only the relevant parts of the
representation.
Make error more informative
Fix up some GUI types
Start to add framework types