client: Bitcoin wallet Client

[buck54321]

The DEX wallet will need a client to interact with a bitcoin wallet. This will likely be a wrapper around the necessary methods of rpcclient pointing to a btcwallet.

• Sync UTXO set (ListUnspent)
• Signing UTXO data (SignMessage)
• Signing transaction inputs (SignRawTransaction)
• Broadcasting transactions (SendRawTransaction)
• Building the swap and redemption transactions

Ideally, the wallet will translate between some common type used by the higher-level DEX wallet infrastructure, and the btcd/rpcclient types. Those common types, and an interface for common wallet client functionality can be specified during this work (and with #36).

This component should be viewed as a plugin component of what could be a simple CLI program or a larger multi-wallet. It is not a stand-alone swap negotiator, so shouldn't be concerned with the negotiation details.

If possible, the wallet should be designed such that it can be reused for bitcoin clones. See ReadCloneParams for more info.

[buck54321]

I'll take this.

[buck54321]

Closed by #72