Token: optionally restrict transferability

[izqui]

Still very much a WIP

Adds the option to flip a switch in a Govern Token to limit which entities can transact with the token, useful for a bunch of experiments

To do:

• [ ] Consider renaming minter to authority or directly using ACL in Token for greater permission granularity
• [ ] Test
• [ ] Comments/docs

J 💪🦅♥️