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
}
				formPageList = sortFormPageList( formPageList );
			}
			return merged;
		}
		public FormPageDef getPage( int index )
		{
			return (FormPageDef) formPageList.get( index );
		}
		public FormPageDef getPage( String id )
		{
			for ( Iterator itor = formPageList.iterator( ); itor.hasNext( ); )
			{
				FormPageDef page = (FormPageDef) itor.next( );
				if ( page.id.equals( id ) )
				{
					return page;
				}
			}
			return null;
		}
	}
	private HashMap editorContributorMap;
	private static EditorContributorManager instance = null;
	private EditorContributorManager( )
	{
	}
	public static EditorContributorManager getInstance( )
	{
		if ( instance == null )