Add handling of app deep links

[kennymc-c]

This adds support for handling app deep links (https://pyatv.dev/development/apps/#app-deep-links)

While testing this I also noticed than entering a custom source parameter when there's also a source list is a little tricky in the web configurator. When you enter any text in the source field it's obstructed by the source list.

[zehnm]

Thanks for adding deep link support!
The check if it's an available app or a deeplink could be beautified, but it's also ok this way.
I will merge it later if you don't want to change it.

[zehnm]

Instead of abusing exception handling to check if app_name exists, check if the name is in _app_list and let @async_handle_atvlib_errors take care of all exceptions:

        if app_name in self._app_list.keys():
            # Launch app by name
            await self._atv.apps.launch_app(self._app_list[app_name])
        else:
            # If app_name is not an app name handle it as app deep link url
            await self._atv.apps.launch_app(app_name)