recreated after branch deleted: because of #286

make the detailed policy ID match the signature algorithm and its other implications.

* implement oroulet changes

* closing_task must be a task not onl run once

* do not catch CancelleError in closing_Task

* make sure we use the correct loop in asyncio binary_server
Co-authored-by: Joey Faulkner <joeymfaulkner@gmail.com>

accidentally wrote PostWrite instead of PreWrite

* 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

* add write subscribe option and 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

* add user to write callback

* allow callbacks to be asynchronous

* remove certificate handler and deal with permissions exclusively with CertificateUserManager

* remove commented out code

* add ability to find endpoints for unauthenticated user

* add pytest mock to travis file

* try to make the file less complex to pass tests

* add pytest mocking to setup.py tests_require

* rename callback dispatcher to callback service

* implement 2/3 changes requested

* fix tests

* add callbacks before write and before/after read

* fix callback tests (i think)

Iterating over the references list and deleting inside the same list
resulted in dangling inverse references if nodes where deleted.

Fix this by iterating over a copy of the references list.

Was previously fixed in https://github.com/FreeOpcUa/opcua-asyncio/commit/4da3e7e827309fe5ffe17bb5f6d84ed56b0dcf6e and subsequently reverted in https://github.com/FreeOpcUa/opcua-asyncio/commit/4268d68595f02b2ae098d9f2844788ec4b4efe21.

Resolves issue #263