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
{
					EditorContributor editorContributor = createEditorContributor( elements[i] );
					if ( !editorContributorMap.containsKey( editorContributor.targetEditorId ) )
					{
						editorContributorMap.put( editorContributor.targetEditorId,
								editorContributor );
					}
					else
					{
						EditorContributor exsitContributor = (EditorContributor) editorContributorMap.get( editorContributor.targetEditorId );
						exsitContributor.merge( editorContributor );
					}
				}
			}
		}
	}
	private EditorContributor createEditorContributor(
			IConfigurationElement element )
	{
		EditorContributor editorContributor = new EditorContributor( );
		editorContributor.targetEditorId = loadStringAttribute( element,
				ATTRIBUTE_TARGET_EDITOR_ID );
		editorContributor.formPageList = sortFormPageList( createFormPageDefList( element ) );
		return editorContributor;
	}
	private static List sortFormPageList( List formPageList )
	{
		List list = new ArrayList( formPageList.size( ) );
		Map relativeMap = new HashMap( );
		for ( Iterator iter = formPageList.iterator( ); iter.hasNext( ); )