Signers without redux

[WIP]

Remove all redux dependencies from signers.

• plugin-signer-account
• plugin-signer-default
• plugin-signer-qr (Maciej handles it)
• plugin-signer-hardware

To update a signer (cc Maciej)

1. Update the ref to your plugin-signer-* repo in package.json
2. Uncomment this line

(For dev purpose, I actually found it simpler to copy the plugin-signer-* files in the shell/src/ folder, and dev from here.)

Should be good!

Note: the old signing logic is separated into small parts, each signer-* handling its own requests.