[Save] Add class for handling modified views

Add a single class to handle saving or discarding
modifications to objects when switching views.
Permits behavior currently replicated across
multiple classes to be consolidated for easier
maintenance, which will simplify resolution of
nasa/mct#243.
[Save] Hook in shared view modified dialog

Utilize the same view modified dialog from
the various places where this dialog needs
to be popped up.
[Save] Allow variable view modified message
[Save] Add Cancel option to view modified dialog

Add back in a Cancel option to the shared
view modified dialog.
[Save] Avoid redundant popup from view switcher

From view switcher, only try to update the
Inspected view on the item event associated
with making a new selection (thus ignoring
the event associated with deselecting the
prior selection); this avoids popping up
a second view modified dialog to the user
if they have Cancelled the first one.
[Save] Use Save action from View Modified dialog

Use the Save action from the View Modified
dialog, instead of partially replicating
its behavior. This should resolve
nasa/mct#243, as the Save action correctly
considers those cases, and additionally
should reduce the likelihood of similar
issues arising in the future.
[Save] Amend unit tests for view modified dialogs

Amend units tests for view modified dialogs
to match pre-conditions and options available
for consolidated view modified dialog.
[Save] Add JavaDoc to view modified dialog
Merge pull request #267 from VWoeltjen/mct243

[Save] Obey policy from View Modified dialog