Bug 120218 Right click menu option to apply theme.
We should support the following right click menu. -- User right clicks int he report design layout area. -- The following menu items needs to be supported Theme --> Apply Theme -->Theme1 -->Theme2 ( similar to Apply style menu option )
UI/org.eclipse.birt.report.designer.core/src/org/eclipse/birt/report/designer/util/DEUtil.java
return elementDefn.getProperty( propertyName );
		}
		return null;
	}
	/**
	 * Gets the proper expression for the given model
	 * 
	 * @param model
	 *            the given model
	 * @return Returns the proper expression for the given model, or null if no
	 *         proper one exists
	 */
	public static String getExpression( Object model )
	{
		if ( model instanceof ParameterHandle )
		{
			return IReportElementConstants.PARAMETER_PREFIX
					+ "[\"" + escape( ( (ParameterHandle) model ).getQualifiedName( ) ) + "\"]"; 
		}
		if ( model instanceof DataSetItemModel )
		{
			String colName = ( (DataSetItemModel) model ).getAlias( );
			if ( colName == null || colName.trim( ).length( ) == 0 )
			{
				colName = ( (DataSetItemModel) model ).getName( );
			}
			return getColumnExpression( colName );
		}
		return null;
	}