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
* (non-Javadoc)
	 * 
	 * @see org.eclipse.birt.report.model.core.Structure#handle(org.eclipse.birt.report.model.api.SimpleValueHandle,
	 *      int)
	 */
	public StructureHandle handle( SimpleValueHandle valueHandle, int index )
	{
		return new LevelAttributeHandle( valueHandle, index );
	}
	/**
	 * Validates this structure. The following are the rules:
	 * <ul>
	 * <li>The column name is required.
	 * </ul>
	 * 
	 * @see org.eclipse.birt.report.model.core.Structure#validate(Module,
	 *      org.eclipse.birt.report.model.core.DesignElement)
	 */
	public List validate( Module module, DesignElement element )
	{
		List list = super.validate( module, element );
		if ( StringUtil.isBlank( name ) )
		{
			list.add( new PropertyValueException( element, getDefn( )
					.getMember( NAME_MEMBER ), name,
					PropertyValueException.DESIGN_EXCEPTION_VALUE_REQUIRED ) );
		}
		return list;
	}
}