Add datetime helpers and move all time/date time datetime_handling folder

previous string_handling located datetime and timestamp files have been moved
to the datetime handling folder

Update readme file with more information about currently covered areas

test-run/progress/progress_test.py

@@ -10,7 +10,8 @@ import sys
 import io
 from pathlib import Path
 from corelibs.file_handling.progress import Progress
-from corelibs.string_handling.datetime_helpers import convert_timestamp, create_time
+from corelibs.datetime_handling.datetime_helpers import create_time
+from corelibs.datetime_handling.timestamp_convert import convert_timestamp
 
 
 def main():