Designer support for adding and navigating to page methods

The designer here has two main jobs: 1) Modifying the properties of the TargetProperties objects to remove the "TargetControlID" property and add the Control converter. We remove "TargetControlID" because the value will be hanging off of the target control's properties already so it's confusing/redundant. 2) Modifying the name of the Extender property so it's user-configurable.

public class ExtenderControlBaseDesigner<T> : ExtenderControlDesigner, 
	IExtenderProvider
where T : ExtenderControlBase

Public Class ExtenderControlBaseDesigner(Of T As ExtenderControlBase) _
	Inherits ExtenderControlDesigner _
	Implements IExtenderProvider

generic<typename T>
where T : ExtenderControlBase
public ref class ExtenderControlBaseDesigner : public ExtenderControlDesigner, 
	IExtenderProvider