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
{
			synchronized ( ExtensionPointManager.class )
			{
				if ( instance == null )
				{
					instance = new EditorContributorManager( );
				}
			}
		}
		return instance;
	}
	/**
	 * Gets the list of all the extended element points.
	 * 
	 * @return Returns the list of all the extended element point
	 *         (ExtendedElementUIPoint).
	 */
	public EditorContributor[] getEditorContributors( )
	{
		synchronized ( this )
		{
			if ( editorContributorMap == null )
			{
				createEditorContributorMap( );
				if ( editorContributorMap == null )
				{
					return null;
				}
			}
		}