Nc-py-api

As the project moves closer to `beta`, final unification changes are being made.
This release contains some breaking changes in `users`, `notifications` API.

Added

- Support for users avatars(`get_avatar`). 149
- `__repr__` method added for most objects(previously it was only present for `FsNode`). 147

Changed

- `users.get_details` renamed to `get_user` and returns a class instead of a dictionary. 145
- Optional argument `displayname` in `users.create` renamed to `display_name`.
- The `apps.ExAppInfo` class has been rewritten in the same format as all the others. 146
- `notifications.Notification` class has been rewritten in the same format as all the others.

Fixed

- `users.get_details` with empty parameter in some cases was raised exception.
- ClientMode: in case when LDAP was used as user backend, user login differs from `user id`, and most API failed with 404. 148

Added

- CalendarAPI with the help of [caldav](https://pypi.org/project/caldav/) package. #136
- [NotesAPI](https://github.com/nextcloud/notes) #137
- TalkAPI: `list_participants` method to list conversation participants. 142

Fixed

- TalkAPI: In One-to-One conversations the `status_message` and `status_icon` fields were always empty.
- Missing CSS styles in the documentation. 143

Added

- TalkAPI:
* `send_file` to easy send `FsNode` to Talk chat.
* `receive_messages` can return the `TalkFileMessage` subclass of usual `TalkMessage` with additional functionality.
- NextcloudApp: The `ex_app.verify_version` function to simply check whether the application has been updated.

Changed

- NextcloudApp: Updated `info.xml` in examples to reflect upcoming changes in the [AppStore](https://github.com/nextcloud/appstore/pull/1145)

Added

- FilesAPI: [Chunked v2 upload](https://docs.nextcloud.com/server/latest/developer_manual/client_apis/WebDAV/chunking.html#chunked-upload-v2) support, enabled by default.
- New option to disable `chunked v2 upload` if there is a need for that: `CHUNKED_UPLOAD_V2`
- TalkAPI: Poll API support(create_poll, get_poll, vote_poll, close_poll).
- TalkAPI: Conversation avatar API(get_conversation_avatar, set_conversation_avatar, delete_conversation_avatar)

Changed

- Default `chunk_size` argument is now 5Mb instead of 4Mb.

Added

- NextcloudApp: `ex_app.persistent_storage` function that returns path for the Application persistent storage.
- NextcloudApp: `from nc_py_api.ex_app import persist_transformers_cache` - automatic use of persistent app directory for the AI models caching.

Added

- FilesAPI: `FsNode.info` added `mimetype` property.

Changed

- AppEcosystem_V2 Project was renamed to App_API, adjust all routes, examples, and docs for this.
- The Application Authentication mechanism was changed to a much simple one.