Abstract the Elliptic Curve used; setup initial testsuite.

* Introduce crypto_util.BTC_CURVE as the curve's name. Replace any
  magic strings in the codebase with crypto_util.BTC_CURVE.
* Invoke pyelliptic.OpenSSL to get curve ID
* Abstract the key length.
Abstract and test public and private key processing.

* pubkey_to_pyelliptic now returns key in bin format.
* Replace hexToPubkey with pubkey_to_pyelliptic.
Create and test a Cryptor class to abstract pyelliptic.

* Replace makePubCryptor, makePrivCryptor and ec.ECC with Cryptor.
* Provide the ECC key getters; do not keep the keys in Cryptor class.
* Purge pyelliptic imports outside crypto_util.
* Purge most references to _myself; replace the rest with cryptor.
Friendlier error when using wrong --dev-mode params.

User is told in friendly english if she forgot to pass the server ip
when using development mode. Now development mode automatically
disables STUN check and UPnP.

Updated usage() string.

Now usage() is printed with new command 'openbazaar help'
unrelated pep8 fixes
fix on dev mode and private ip check

make one node a seed when on --dev-mode, let the other N-1
nodes know about the one seed.
Merge pull request #817 from gubatron/friendlier-dev-mode-error-and-help-command

Friendlier `--dev-mode` error message, new `help` command
PEP8 cleanup of ws.py
PEP8 cleanup on openbazaar_daemon.py
Merge pull request #825 from rdtaylor/pep8_openbazaar_daemon

PEP8 cleanup on openbazaar_daemon.py
Merge pull request #824 from rdtaylor/pep8_ws

PEP8 cleanup of ws.py
Merge pull request #735 from Renelvon/refactor_crypto_util

Refactor and test crypto_util. Wrap pyelliptic.
Refactor network_util; use it in DHT.

* Test for private address using IPy.
* Abstract protocol in get_peer_url.
* Prefer importing modules than names.
* Drop unused imports.
* Other style fixes.
Refactor code in connection.py.

* Drop unused attributes _peer_alive and responses_received.
* Make failure cases stand out in send, send_raw and start_handshake.
* Drop PeerListener.stop.
  * Do not destroy global context arbitrarily.
  * Turn TransportLayer.shutdown into abstract method.
* Straighten PeerListener.listen.
* Make default callbacks equal to None.
* Catch ValueErrors produced by json.loads.
* Assert the sender's guid has been initialized prior to sending.
* Remove unused import.