Add hardware wallet support

[Thegaram]

What problem are you trying to solve?

Add hardware wallet support. I would like to be able to manage my conflux keys on a hardware wallet and sign transactions with it.

Describe the solution you'd like

Given that Conflux is mostly compatible with Ethereum, I think existing hardware wallets might work out of the box. Is it possible to enable this feature from MetaMask on Conflux Portal so that users can sign transactions using their hardware devices?

The way this works is something like this: Conflux Portal reads public keys from device and derives the addresses. When sending a transaction, Conflux Portal sends a sign transaction request to the wallet.

Additional context

In order for CFX to show up in the associated hardware wallet dashboards, we might need to modify their firmware (see [here] and [here]). However, using devices just for signing on Conflux Portal might work out of the box. For now, this would mean using the same accounts on Conflux as one uses on Ethereum. Later we can add full integration to popular hardware wallets.

Conflux uses a slightly different approach to deriving addresses from public keys (0x1 prefix for normal accounts, 0x8 for contracts), see equation (1) from the spec.