Bug 188578 Add "displayColumnName" on TabularLevel
Add Property "displayColumnName" on TabbularLevel and corresponding APIs on handle. Property Type: expression.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/api/olap/TabularLevelHandle.java
* @param element
	 *            the model representation of the element
	 */
	public TabularLevelHandle( Module module, DesignElement element )
	{
		super( module, element );
	}
	/**
	 * Gets the column name of this level.
	 * 
	 * @return column name of this level
	 */
	public String getColumnName( )
	{
		return getStringProperty( COLUMN_NAME_PROP );
	}
	/**
	 * Sets the column name for this level.
	 * 
	 * @param columnName
	 *            the column name to set
	 * @throws SemanticException
	 *             property is locked
	 */
	public void setColumnName( String columnName ) throws SemanticException
	{
		setStringProperty( COLUMN_NAME_PROP, columnName );
	}
}