For overlays that do not need to do special things when a
window is dismissed, provide a default cancel function.
This simplifies implementation of the information-only
dialogs, such as the About dialog, WTD-667.
Fill in specs for bundle platform/commonUI/dialog,
which provides the ability to show dialogs. One
of the common user interface elements being transitioned
for WTD-574.
Refactor bundle platform/commonUI/dialog such that
the concerns of showing dialogs (including showing
a single instance thereof) and managing changes to
the DOM are more cleanly separated. This simplifies
testing and satisfies code style guidelines for
this bundle, in preparation for its inclusion among
common user interface bundles to be transitioned
in WTD-574.
Add in-line documentation to the dialog service,
exposed by bundle platform/commonUI/dialog, one
of the common user interface bundles being
transitioned for WTD-574.
When a dialog is already showing, act as if the
user input was cancelled and show a warning.
Part of ongoing transition of common user interface
bundles for WTD-574.
