Revision 615

Now that we can depend on the order in
        a Classification and have methods to manipulate that order we don't
        need to use our own data structures in the grid. We can simply make
        the grid/table access the information they need from a copy of
        the classification object.
(Classifier._OnCloseBtn): Event handler for when the user clicks
        'Close'. This is needed so if the user applies changes and then
        continues to change the table the user has the option of discarding
        the most recent changes and keeping what they applied.