Urbanairship

- Adds package type annotations
- Adds ability to specify a custom base url when creating client
- Updates various dependencies and build process
- Removes deprecated client classes and create functions. See documentation for new approach.

- Adds Support for OAuth2 Authentication
- Adds new client classes for BasicAuth, BearerTokenAuth, and OAuth
- Deprecates the Airship client class in favor of the new client classes

- Adds Support for iOS Live Activity and Android Live Update
- Adds new class `ConnectionFailure`
- Adds `bypass_holdout_groups` parameter for push options

- Adds Support for Tag Lists using the `urbanairship.TagList` class

- Removes support for Python 2. New minimum Python versions is 3.6
- Removes support for location APIs
- Removes LocationFinder class
- Removes location-based audience selectors: location, recent_date, absolute_date
- Adds `token` property to `urbanairship.Airship` to support bearer token API authentication
- Adds optional `retries` property to urbanairship.Airship to specify number of times to retry failed API requests
- Adds CustomEvent class for sending custom events
- Adds SmsCustomResponse class
- Adds type annotations for function and method signatures

- Adds Custom Event Reports
- Adds Experiments Overview and Variant Reports
- Adds Scheduled Experiment Listing
- Adds Web Response Reports
- Adds opt_in_mode and properties to Email class
- Adds email attachments support in the EmailAttachment class
- Adds mms audience override
- Adds shorten_links support to sms and mms sends
- Adds support for SMS keyword interactions in the KeywordInteraction class
- Adds update method to Email class
- Adds update method to Sms class
- Adds support for push validation
- Adds email association and disassociation to NamedUser class
- Adds Named User uninstall, attributes, and update methods
- Adds message_center_delete class method to Push class
- Adds schedule_exclusion
- Adds recurring_schedule and ScheduledPush.recurring
- Adds pause and resume methods to ScheduledPush for recurring schedules
- Adds validate method to ScheduledPush
- Adds support for push and scheduled push localization
- Adds SubscriptionList class for subscribing and unsubscribing audiences
- Adds subscription_list and static_list audience selectors
- Adds AttributeList class with methods for create, upload, get_errors, and list
- Adds download class method to StaticList class

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