Messente-api

What's Changed
* Add error 401 to Omnimessage API


**Full Changelog**: https://github.com/messente/messente-api-python/compare/1.4.2...1.5.0

What's Changed
* Add parameter ttl to Omnichannel API message sending request. This allows the users to specify the validity period of a message in the unit of seconds (as opposed to minutes for the validity field). Preserves backward compatibility with validity.

Generated code with https://www.npmjs.com/package/openapitools/openapi-generator-cli/v/2.1.17's `python-legacy` v5.0.0 generator:

- Docs changed
- `ApiException` subclasses were added:

<img width="1109" alt="Screenshot 2021-01-18 at 19 46 25" src="https://user-images.githubusercontent.com/26983671/104949126-1aec7480-59c7-11eb-99b7-70a0fdfb612c.png">
- Models' `to_dict` changed:

<img width="1258" alt="Screenshot 2021-01-18 at 19 56 12" src="https://user-images.githubusercontent.com/26983671/104949241-4ec79a00-59c7-11eb-9de7-15fbf5e21c34.png">

Add an optional `priority` field to Omnichannel API message sending request. This field sets the priority of the message. Messages are processed starting with in highest priority queue first and lowest priority queue last. This for example allows to prioritize OTP messages over marketing traffic.

The new field has three possible values:

- low,
- regular,
- high.

**Bug Fix**

[phonebook-api][contacts] Make sure scheduled deletion date field is only in responses, not in requests

**Added Functionality**

- [phonebook-api][contacts] Add scheduled deletion date to response
- The date (in ISO 8601 format, YYYY-MM-DD) on which the contact is going to be deleted because it has not belonged to a group for 30 days
- [statistics-api] Allow fetching Telegram statistics


**Bug Fixes**

- [omnichannel-api] Declare error item source nullable
- [omnichannel-api] Make cancelling a message return an empty object