[Delete] Allow custom message objects in dialogs

Support (by way of hints) injecting custom message
components (Swing components) into input/message
dialogs shown through the WindowManagerImpl.

This is useful for delete all specifically, as its
warning messages may contain lists of components
which are going to be deleted (for example)
[Delete] Use Window Manager for Delete All dialog

Use the Window Manager (as opposed to static methods
of OptionBox) to show the warning dialogs related
to the Delete All action introduced for nasa/mct#89.

This slightly reduces the explicit Swing
dependencies associated with the action and
facilitates automated testing of interactions
(the WindowManager can be mocked, but the static
methods of OptionBox cannot). These are ongoing
concerns of nasa/mct#155.
[Delete] Hoist platform references in Delete All