Add Weekdays configuration option to sessions

Update TimeRange to include weekdays

- add weekdays slice as field to TimeRange
- update constructor to remove possible panic, instead return error
- update tests now the TimeRange constructor now returns an error
- convert tests to table test format

Update sessionFactory to set weekdays property

- update code that creates TimeRange to handle errors
- read and set the Weekdays value if provided, erroring if it is given
  with StartDay/EndDay.

Update session_test to handle timerange error