Remove the need for didReceiveLocalNotification when using the UILocalNotification APIs (iOS version < 10)

[MaikuB]

Current advice is for developers using the plugin to handle the didReceiveLocalNotification method within the app delegate of their iOS head project. In theory, it should be possible to handle this within the plugin itself since the plugin is registered as an application delegate. However, the method never fires when trying to handle it within the plugin.

This has been raised on the Flutter repository flutter/flutter#16662 for the Flutter team to look into. Suggest anyone that would like the Flutter team to look into it to vote with a thumbs up as this seems to be how they prioritise looking at issues