[BC/CWC] Wallet private key updates [1]

[MichaelAJay]

bitcore-client

Encryption

• adds encryptBuffer - enables normalized buffer input
• adds decryptToBuffer - enables improved security by not decrypting directly to string

Storage

• adds addKeysSafe - incoming keys' private key is encrypted, so not immediately available to be used to retrieve pubkey, which should be available anyway. Throws if missing a pubkey

Wallet

• Adds version: 2 & version checks for backwards compatibility (note: to create an old Wallet would require version: 0 - so 1 is skipped - looking for feedback on numbering/versioning).
• create encrypts HDPrivateKey xprivkey and privateKey so they can be decrypted as buffers instead of serializing the whole masterKey and THEN encrypting
• importKeys does the same for signing keys
• signTx decrypts to buffers then uses deriver for chain-aware decoding. In the next phase, this decoding should be made unnecessary by passing the buffer all the way through to use, if possible

Tests

• update prior tests to include versioning
• introduce new tests for version 2 specifics

crypto-wallet-core

Derivation

• Add two passthrough methods on DeriverProxy to buffer & serialize private keys
• Adds privateKeyToBuffer and privateKeyBufferToNativePrivateKey to IDeriver & implement for each Deriver - no need to override for any of the extending classes (UTXOs to AbstractBitcoreLibDeriver & EVM to EthDeriver)