Pybankid

* Removal of some leftover SOAP v4 API code
* Multiple corrections for exceptions
* Improved documentation
* Added Python 3.9 in CI testing

Changes

- Update relying party guidelines PDF link to version 3.5 (33)
- Update link to test cert (32)
- Dependabot config (31)

- Corrections for some changed RFA details in documentation.
- Moved CI from Azure Pipelines to Github Actions.

Fix for bug where `userNonVisibleData` was erroneously handled in the JSON Client (14).

BankID has release a `v5` version of their API, exposing a REST API returning JSON data. A new PyBankID RP client class, `BankIDJSONClient`, has been implemented to use this API in favour of the SOAP API of `v4`.

Features
- JSON based interface client added. Solves 12.
- Added PendingDeprecationWarning to BankIDClient.
- Updated documentation
- Testing only on 2.7, 3.5, 3.6 and pypy

Minor fixes
- Added legacy mode to BankIDClient test server as well.
- Updated tests
- Improved `certutils`.

Fixes
-------
- Corrected macOS High Sierra bug in `certutils`
- Added PyPy to Travis testing.
- Updated `setup.py`