DE10: Slots can't be removed from packages, from "Edit Properties" menu
on packages 
https://rally1.rallydev.com/slm/detail/df/18901585530
DE11: Package diagram: sub-package properties dialog needs scroll bar 
https://rally1.rallydev.com/slm/detail/df/18938168534
Task US2: Export file groups from packages 
https://rally1.rallydev.com/slm/detail/ar/18901923777

Add the exportFileGroupToSlot() method (and associated methods) to allow
file groups to be inserted into a package's output slots.