INotifyPropertyChanged: Introduce a standardized mechanism for this #52
Description
In the same vein of thought we should employ this inside
labeled.dropdown/control.builder.lua
To improve the way we intercept changed-events from the native pfui-control (frame). The current implementation is somewhat suboptimal in the sense that we are only alerted on initial-display of the control and on user-initiated changes. If the value store changes behind our backs via direct storage manipulation then no notification will be received (rare scenario but not inconceivable).