Update underlying data field when related object is updated.

If the selected Library Document is out-of-range throw a specific error
Don't fail if the user clicks on open space in the BookMark list
Added property to provide a right margin (RTBMargin) between the RichTextBox and the StepItem

PROMS/VEPROMS.CSLA.Library/Generated/UserMembership.cs

@@ -88,6 +88,7 @@ namespace VEPROMS.CSLA.Library
 				if (_MyGroup != value)
 				{
 					_MyGroup = value;
+					_GID = value.GID;// Update underlying data field
 					PropertyHasChanged();
 				}
 			}