Fixed bug that didn't allow Product Groups with the same name in
different Storage Units.
Also disallowed bogus create/edit of PGs and SUs even if the GUI doesn't
prevent the user from entering invalid data.
Refactor of Listeners to allow for keeping selections after dialog
actions
Merge branch 'master' of https://github.com/cletusw/hit.git

Conflicts:
	src/gui/productgroup/AddProductGroupController.java
	src/gui/productgroup/EditProductGroupController.java
	src/mcontrollers/ProductContainerListener.java
	src/model/ConcreteProductContainerManager.java
	src/model/ProductContainerManager.java