Postcard-creator

Fixes issues in swissid token authentication by implementing a new anomaly detection endpoint 41

- drop support for postcard_creator_legacy
- update legacy (username/ password) token authentication due to changed endpoints
- note: legacy method now uses postcard_creator_swissid endpoints instead of postcard_creator_legacy, postcard_creator_legacy is out of life

update requests to v2.25.1 to fix "AttributeError: 'NoneType' object has no attribute 'group'" in authentication. 27

- support of new swissid authentication (access_token with code/ code_verifier)
- support of new endpoints at https://pccweb.api.post.ch/secure/api/mobile/v1
- class PostcardCreator is a proxy which instantiates an endpoint wrapper compatible with authentication method of token, underlying wrappers are: PostcardCreatorSwissId, PostcardCreatorLegacy



- migration to v2.0
- with authentication method swissid: if you rely on get_billing_saldo(), get_user_info(): these endpoints return data in different format
- customizations image_target_width, image_target_height, image_quality_factor no longer compatible with authentication method swissid
- require python 3.6 or later