This reverts commit 582ce16e.

Session Type-level Polymorphism

See merge request iris/actris!12

Remove coercion `iMsg_car` and `Proper` instances to avoid one accidentally breaking the `iMsg` abstraction.

- Protocols are no longer contractive in the message
- New type `iMsg` for messages to avoid telescopes in protocols
- Better rules for subprotocols that do not involve telescopes, but allow introduction
  and elimination of quantifiers and the payload
- Better notations for protocols
- Notation ⊑ for subprotocols
- Make ⊑ except-0 so one can strip laters when proving a ⊑
- Restore recursive domain equation to push later inwards to support protocols
  that are not contractive in the mssage.
- Proofmode support for easy manipulation of ⊑

Kinded subtyping, better file structure, more setoid stuff, reorganize imports.

Adding kinded polymorphism in types

See merge request iris/actris!11

Plainly

See merge request iris/actris!10

Copying

See merge request iris/actris!9

Algorithmic Typing Judgement

See merge request iris/actris!8