Issue 14: Implement a connector to Electrum

Created electrum.py which has a tcp-only interface into any electrum
tcp/non-ssl server.

utxodb now uses electrum.py to grab raw data.

To use:

electrum_interface = ElectrumInterface(host, port)
utxo = electrum_interface.get_utxo(address)
raw_tx = electrum_interface.get_raw_transaction(tx_id, height)