Bug 197589 Need constant for automaic attribute name "DateTime"
Currently when set dateTimeLevelType for cube level, model will automatically create a built-in attribute "DateTime". But the name is hard-coded. We need a public constant for this name to allow UI to access it.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/api/elements/structures/LevelAttribute.java
* 
	 * @return the data type of this column.
	 */
	public String getDataType( )
	{
		return (String) getProperty( null, DATA_TYPE_MEMBER );
	}
	/**
	 * Sets the data type of this column. The allowed values are defined in
	 * {@link org.eclipse.birt.report.model.api.elements.DesignChoiceConstants},
	 * and they are:
	 * <ul>
	 * <li>COLUMN_DATA_TYPE_ANY
	 * <li>COLUMN_DATA_TYPE_INTEGER
	 * <li>COLUMN_DATA_TYPE_STRING
	 * <li>COLUMN_DATA_TYPE_DATETIME
	 * <li>COLUMN_DATA_TYPE_DECIMAL
	 * <li>COLUMN_DATA_TYPE_FLOAT
	 * <li>COLUMN_DATA_TYPE_STRUCTURE
	 * <li>COLUMN_DATA_TYPE_TABLE
	 * </ul>
	 * 
	 * @param dataType
	 *            the data type to set
	 */
	public void setDataType( String dataType )
	{
		setProperty( DATA_TYPE_MEMBER, dataType );
	}
	/*