* eslint: Check for unused function arguments
* eslint: Ignore unused '_' in argument list
Also allow any number of '_' e.g., '__' or '___' which is to be used sparingly
* Remove and rename unused arguments
Calls to `personal_sign` are now:
- When hex encoded, preserved as hex encoded, but displayed as utf-8 text.
- When not hex encoded, decoded as utf-8 text as hex for signing.
- The messages proposed for signing are displayed as UTF-8 text.
- When the message cannot be rendered as UTF-8 text, it is displayed as hexadecimal.
Fixes#1173
These external modules now have their own test coverage and build enforcement. This allowed me to somewhat more easily add good tests around our personalSign strategy (held now in [eth-sig-util](https://github.com/flyswatter/eth-sig-util), and allow each of the keyrings to import that, etc.
