This refactors the homescreen state object to isolate drag & drop from
swipe states, allowing for using proper system-level drag & drop for delegate
movement. This then ports the new applet list to use it.
Currently delegates do not get deleted when removed from models. Due to
the complexity of drag state and other objects, we can't simply delete
the delegate when removed from the model because they might still be
involved in animations or other state at the time of removal. Use smart
pointers to have the delegate objects deleted instead.
QML unfortunately doesn't support QSharedPointer, so we need to expose raw pointers to it.
