TimeSeries - optional/obsolete attributes
Created by: gioagu
as discussed yesterday in Munich during the workshop, some attributes in the _TimeSeries need to be removed or changed. In detail:
the id attribute is obsolete and should be deleted.
the temporalExtent (which is not necessary for instance for irregular time series, or regular time series used for a DailySchedule) should be an optional attribute.
in TimeValuesProperties, the qualityDescription and the source should be also optional attributes.
The variableLabel is obsolete since it is already included in GML, and should be then removed.