#230

Remove unused import statements
Make code more PEP8 conform

* getting started

* remove ridiculous change to generated code

* remove ridiculous change to generated code

* checkpoint

* another checkpoint

* found the error, tests now pass

* improve error when person with incorrect credentials tries to connect

* add better error handling for when a user does something they aren't permitted to do

* pass tests

* add tests for simple permissions

* add third certificate and some documentation

* clean up pull request

* remove pointless import

* hopefully pass tests

* implement changes requested

* add dataclasses to requirements for python 3.6

* put dataclasses in the travis file instead of the dev_requirements.txt

* implement user manager in iserver instead of using the certificate handler

* uncomment some code

* add permissions=None to base security policy object

* pass crypto connect tests

* fix tests

* hopefully pass all the tests now

* actually pass tests this time

* remove certificate handler and deal with permissions exclusively with CertificateUserManager

* remove commented out code

Async call method in internal_session
Async history_read method in internal_session
Async get_endpoints method in server
Async delete_nodes method in server and client
Async load_enums in server and client
Async stop method in HistoryManager class
Async load_type_definitions method in server and Client
Async import_xml in server and Client

-Modifies client.py to allow for passing an optional private key password to cryptography to allow loading a password encrypted private key for client authentication.

* fix authenticating server example

* certificate handling working, tests required

* add tests

* add example certificates and remove some useless code

* add client-with-encryption.py to connect with server-with-encryption

--amend

* Add async and await to get_namespace_array methods
Add /venv to gitignore

* Removed Coroutine typing from get_namespace_array methods