Bug 179931 Provide new interface IStyle to let extension return the style properties values
Provide the IStyle interface to let extension user can return the style property value list for their extension elements.
model/org.eclipse.birt.report.model.tests/test/org/eclipse/birt/report/model/extension/PeerExtensionTest.java
assertEquals(
				"11.2mm", extendedItem.getStringProperty( ExtendedItem.Y_PROP ) ); 
		assertEquals(
				"firstDataSet", extendedItem.getStringProperty( ExtendedItem.DATA_SET_PROP ) ); 
		
		assertNull( designHandle.findElement( "testTable" ) ); 
		
		LabelHandle label = designHandle.getElementFactory( ).newLabel(
				"testLabel" ); 
		assertEquals( "testLabel1", label.getName( ) ); 
		designHandle.getBody( ).add( label );
		save( );
		assertTrue( compareFile( "PeerExtensionTest_golden_2.xml" ) ); 
	}
	/**
	 * Tests an extension has 'extensionName' property even if it does not
	 * extend from 'ExtendedItem'.
	 * 
	 * @throws Exception
	 */
	public void testExtensionNameProp( ) throws Exception
	{
		MetaDataDictionary dd = MetaDataDictionary.getInstance( );
		assertTrue( dd.getExtensions( ).size( ) >= 3 );
		ElementDefn extendedCell = (ElementDefn) dd
				.getExtension( "TestingTable" ); 
		assertNotNull( extendedCell );
		assertEquals( dd.getElement( ReportDesignConstants.TABLE_ITEM ),
				extendedCell.getParent( ) );
		PropertyDefn extensionName = (PropertyDefn) extendedCell