Need a way for QML multimedia apps to set the audio stream role

A major use case for Ubuntu Touch is to have the ability for QML apps to be able to set an audio stream role property on common multimedia QML playback classes such as MediaPlayer and Audio. The purpose of this role being a category for grouping certain types of audio streams together so that they can be acted upon as a group, such as changing the volume level of an alarm role while not affecting the volume level of the more general multimedia level (music playback, video playback, etc).