Wallet: deprecates newMasterKey
Wallet: move all free functions out of Wallet scope
Wallet: move estimatePaddedTxFee out of Wallet scope
Wallet: clarify getPrivateKeyForAddress method structure

This does repeat the O(n) lookup several times, but that can be fixed by
using an O(1) lookup instead (and will be later).

Clarity first.
Wallet: rework unspents to primarily work on initialization

The RegExp for the UTXO validation was removed as the errors are now
more verbose and specific to each case.
Wallet: move most instance methods to prototype
Wallet: move createTx to prototype
Wallet: rename masterkey to masterKey
Transaction: deprecate Tx signing methods
TxBuilder: Initial commit and tests
TxBuilder: use data fixtures for invalid tests
TxBuilder: transform all signatures once
TxBuilder: use build/buildIncomplete over boolean
Wallet: use TxBuilder instead
TxBuilder: fix missing code path
TxBuilder: add pubKey test fixture
TxBuilder: add invalid nulldata case
TxBuilder: sign after error checking
TxBuilder: remove unnecessary assert
index: add TransactionBuilder