Merge branch 'fix/rm-default-timestamp' into 'master'

DataFile: Don't write creationDate & updateDate unless specified

See merge request !937

src/cal_tools/files.py

 
-from datetime import datetime
+from datetime import datetime, timezone
 from itertools import chain
 from numbers import Integral
 from pathlib import Path
@@ -311,10 +311,14 @@ class DataFile(h5py.File):
                 sequence = self.__sequence
 
         if creation_date is None:
-            creation_date = datetime.now()
+            creation_date = datetime.fromtimestamp(0, tz=timezone.utc)
+        elif creation_date is True:
+            creation_date = datetime.now(timezone.utc)
 
         if update_date is None:
             update_date = creation_date
+        elif update_date is True:
+            update_date = datetime.now(timezone.utc)
 
         md_group = self.require_group('METADATA')
         md_group.create_dataset(