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
{
		String relativeId = element.relative;
		int i = 0;
		for ( Iterator iter = list.iterator( ); iter.hasNext( ); i++ )
		{
			FormPageDef formPage = (FormPageDef) iter.next( );
			if ( formPage.id.equals( relativeId ) )
			{
				return list.indexOf( formPage );
			}
		}
		return -1;
	}
	private List createFormPageDefList( IConfigurationElement element )
	{
		ArrayList formPageDefList = new ArrayList( );
		ArrayList keyList = new ArrayList( );
		IConfigurationElement[] elements = element.getChildren( );
		for ( int i = 0; i < elements.length; i++ )
		{
			FormPageDef formPageDef = new FormPageDef( elements[i] );
			if ( !keyList.contains( formPageDef.id ) )
			{
				formPageDefList.add( formPageDef );
				keyList.add( formPageDef.id );
			}
		}
		return formPageDefList;
	}
	private List getExtensionElements( String id )