Bug 169025 Supports overridden on editor contribution
After contributting a new editor to the multiPageReportEditor, supports to enable the new editor to override a editor by assigning the ID.
UI/org.eclipse.birt.report.designer.ui.editors/src/org/eclipse/birt/report/designer/internal/ui/extension/EditorContributorManager.java
{
					if ( relativeMap.containsKey( element ) )
					{
						List relativeList = (List) relativeMap.get( element );
						FormPageDef relativeElement = (FormPageDef) relativeList.get( 0 );
						relativePosition = getElementPosition( relativeElement,
								list );
						int position = relativePosition
								- relativeElement.position;
						list.add( position < 0 ? 0 : position, element );
						for ( Iterator iterator = relativeList.iterator( ); iterator.hasNext( ); )
						{
							FormPageDef relativeFormPage = (FormPageDef) iterator.next( );
							list.remove( relativeFormPage );
							list.add( relativePosition
									+ element.position
									+ relativeFormPage.position,
									relativeFormPage );
						}
					}
					else
					{
						addRelativeMap( element, formPageList, relativeMap );
						
						list.add( list.size( ), element );
					}
				}
			}
		}
		return list;