Allow multiple Elements to be added to Selector
Allow multiple Elements to be added to Selector

It maintains the single selected item over all of their children.

This also switches it to use a Value to expose the selected value
instead of two signals, which is way cleaner.

tomfisher/tripleplay,joansmith/tripleplay,joansmith/tripleplay,tomfisher/tripleplay,tomfisher/tripleplay,tomfisher/tripleplay,joansmith/tripleplay,tomfisher/tripleplay,joansmith/tripleplay,joansmith/tripleplay