i223: have calendar default to 'standard' unless overloaded or read from the file

Passing 'standard' as default at the RequestDataset level did not make sense
as it implied the value was overloaded when it in fact was not. The purpose
of those parameters are for explicit overloading.

Also added additional tests for calendar overloading.
Merge branch 'master' into i155-seasonal
minor

Modified test function to return a "TemporalDimension".
mark
mark - before modifying get_grouping
mark - before changing group returning method to iterator
mark - before making sure months are included in the seasons
mark - start of day