Implement Passphrase autogeneration and a trivial key handling refactor

[brxken128]

This branch trivially refactors how keys get their "secrets", by adding a Key struct. You may use Key::get_secret() to get the secret value, and the logic for this is contained within parameters.rs.

Passphrase auto-generation was added using the EFF Large Wordlist, just with the index removed. This will cause the Dexios binary to increase marginally in size, but that's nothing compared to the benefits gained.

Currently, the generated password looks something like: Surcharge-Otter-Backpedal-574345. It is shown once during generation, and never again. 3 large capitalized words, separated with -, and 6 numbers at the end.

This may change in the future, but keys will always be compatible (and with V4 headers, you can change them!)