Many widget classes need to run substantial initialization code after
they have been setup from GML. With this change, an
initialize_fallibles() function is called if available, allowing the
initialization to be invoked from the GML setup automatically. This
means that the GML-generated creation function can now be used directly
for many more cases, and reduces code duplication.
Add a new widget "DynamicWidgetContainer" that is used to group it's
child widgets within an collapsable and detachable container. The
DynmnicWidgetContainer is able to persist it's view state if a config
domain has been provided. Having that set will allow the widget to
restore it's view state automatically.
