Custom wordlist support

[piegamesde]

Since the protocol allows for arbitrary passwords, clients can already use arbitrary wordlists. However for good interoperability and especially tab completion or form input validation, some protocol support is required.

Client specific discussion threads:

• https://github.com/magic-wormhole/magic-wormhole.rs/issues/106
• https://github.com/magic-wormhole/magic-wormhole/issues/301
• https://github.com/magic-wormhole/magic-wormhole/issues/426
• https://github.com/magic-wormhole/magic-wormhole/issues/26

I'd like to not discuss actual alternative wordlists here (yet), but instead first decide onto how the protocol should be expanded. https://github.com/magic-wormhole/magic-wormhole/issues/26 already covers some ground there.

[donpui]

We could also think from peoples with disabilities aspect, can some changes in protocol be made to support such development.

[piegamesde]

Which people with which disabilities and what changes in the protocol?