DHT._dataStore -> DHT.dataStore
DHT/Transport refactors, updates.

 - DHT on_find_node DRY refactors.
 - TransportLayer/CryptoTransportLayer now destroy ZMQ sockets on shutdown.
Wrap long lines: node/constants.py
Wrap long lines: test/test_ec.py
Wrap long lines: test/test_dbstore.py
Wrap most long lines: node/arithmetic.py
Wrap most long lines: node/connection.py
Wrap most long lines: node/datastore.py
Wrap most long lines: node/db_store.py
Wrap most long lines: node/multisig.py
Wrap most long lines: node/openbazaar_daemon.py
Wrap most long lines: node/upnp.py
Wrap most long lines: node/ws.py
Use small hanging indents: node/dht.py
Use small hanging indents: node/market.py
Use small hanging indents: node/transport.py
Enable flake8 style check for hanging indents.
Bump flake8 version.