feature: password-agent: password derivation for trezor devices

[f321x]

Implements a new feature, password-agent, which allows to derive passwords and mnemonic passphrases from the hardware wallet.
This can be useful to obtain high entropy passwords for things like file encryption.
The user provides a context string, e.g. gmail, confirms a signature on the hardware wallet and (with default args) receives a mnemonic passphrase.

Examples:

Default usage:
$ trezor-password gmail
> carton-unviable-backless-polo-steam-unwound-rocking-banister-polygon-ivy

Base 58 encoding with -b58 or --base58:
$ trezor-password gmail -b58
> 5B8qjnGqseE4KTb7CHCiRJ!

Raw hex output with --raw or -r:
$ trezor-password gmail --raw
> 21ced2f820074f2d557ab4aeea1a7b5d

Providing a custom wordlist with -w or --wordlist:
$ trezor-password gmail -w wordlist-german.txt
> Einweisens-Westinsel-Flugdatenprozessors-Fliegervereine-Säumer-zeitinvariantes-Softwaretitels

Currently it is only exposed for Trezor devices. I was testing with a Ledger Nano S as well, however it refused to sign my message, may investigate Ledger again if this gets merged.

[f321x]

Rebased from 9c72dd9 to 0745a22.
Should fix the pycodestyle CI issues.

[f321x]

Rebased from 0745a22 to d903eab.
Forgot to commit the changes to test_password.py. Now pycodestyle should be happy :)

[f321x]

Rebased from d903eab to 65fc9bb.
Now i ran the CI in my fork, should definitely pass.

[romanz]

Why not to use passage for generating and encrypting the passwords?
It works with age whose decryption can be offloaded to Trezor:
https://github.com/romanz/trezor-agent/blob/master/doc/README-age.md

[f321x]

The difference to a password manager is that this is kind of stateless.
The only input required to derive a password is the context string, which can follow a certain scheme like using the url or name of some service the password is intended for. This eliminates the need to back up any additional files like the database of the password manager, and comes with different trade-offs than a password manager.