Port hdwallet to be Synapse compatible

[meyer9]

Update github.com/btcsuite/btcutil to be Synapse compatible.

Specifically, do the following:

• Move the hdkeychain folder into synapse wallet folder.
• Remove references to chaincfg.Params and replace with constants that already exist in Synapse code
• Replace btcec.Pubkey/PrivateKey with secp256k1.PublicKey/PrivateKey