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
Dan Finlay