Desktop-notifier

Added:

* You can now set interaction callbacks at the `DesktopNotifier` level which will be
called on interactions with any notifications from the running app. Callbacks set on
an individual notification take precedence if set.

Changed:

* `send` methods now return the notification ID instead of the notification instance.
* Notification objects are fully immutable.

Fixed:

* Callbacks on notification dismissal not being called on macOS.

Deprecated:

* Setting `notification_limit` will be ignored and logs a deprecation warning.

Removed:

* Deprecated APIs from v5.0.0.

Fixed:

* Fixed compatibility of type annotations with Python 3.8.

Added:

* Support for custom notification sounds on all backends.
* Allow specifying sounds and icons either by name (for existing system sounds) or as a
referenced by a URI or path.
* Allow specifying attachments either by URI or path.
* Add a `get_capabilities()` API that returns which features are supported by a
platform.
* Compatibility with Ubuntu 20.04 and other older Dbus notification servers which do not
conform to the current desktop notification API spec.
* A dedicated class `DesktopNotifierSync` with a blocking API instead of the async API
of `DesktopNotifier`.

Changed:

* Removed code signing requirement for macOS binaries. Instead of preventing
notification requests, only log a warning that notifications may fail. It is not
documented which code signature checks an app must pass to send notifications and this
allows apps that fail some of the checks and still send notifications.

Fixed:

* Fixed a segfault on macOS when passing an attachment path that does not refer to an
actual file.

Deprecated:

* Deprecated specifying icons as strings. Use the `base.Icon` class instead.
* Deprecated specifying attachments as URI strings. Use the `base.Attachement` class
instead.
* Deprecated specifying notification sounds as boolean (`True` = default sound,
`False` = no sound). Use `base.DEFAULT_SOUND` for the system default and `None` for no
sound instead. Use the `base.Sound` class for custom sounds.

Removed:

* Removed the synchronous `DesktopNotifier.send_sync()` API. Use `DesktopNotifierSync`
instead.

* Require winrt>=2.0, the first stable release of the Python to WinRT bridge.
* Fail gracefully when call for authorization fails on Windows with an OSError.
* Added type checking to Windows backend.
* Removed support for NSUserNotificationCenter. This means that macOS 10.13 and older
are no longer supported.

* Remove importlib_resources dependency in favour of stdlib importlib.resources. This
also fixes a breakage due to API changes in importlib_resources>=6.0.

* Fixes an issue with the `on_clicked` callback being shown as a button with label
"default" on Xfce desktop environments.