Tabbed terminals

Elementary introduction of tabbed terminals.
It's a cleaner way of letting the tab manage QML component lifecycle. QML for each tab is loaded and those components setup only once they're activated for view. See [Dynamic QML Components](http://developer.blackberry.com/native/documentation/cascades/best_practices/dynamic_qml/index.html). From a practical standpoint, it'll make deleting tabs easier as we can just let QML do its own thing in deactivating and then deleting delegates.