Batch updates to undo history

[MarkMpn]

• Implement ISupportsInitializeNotification interface in base control. While control is being initialized, no changes (being triggered by the control being populated) trigger a call to Save and so do not appear in the undo history
• A similar process using the Initializing field was already added to reduce flicker on the conditionControl, so moved this to use the ISupportsInitializeNotification mechanism for consistency
• Also use BeginInit / EndInit to batch multiple changes being made by selecting a relationship so this appears only once
• Added property to SaveEventArgs to indicate if change is being triggered by a keypress event or not. Keypress-generated events are ignored from undo history
• Add & remove event handlers as necessary so Save event is still triggered on each keypress to update the rest of the UI but adds an extra event handler to Validated event to trigger an extra Save call when the user finishes editing the field so it can be added to undo history.