Refs #9244.  Made changes according to code review

used m_values.back() instead of first *m_values.rbegin() at line 840;
removed the outdated comment at line 1182;
Made change according to code review. Refs #9244.

1. Add a case in addValue to switch from unknown to unsorted;
2. Fixed an indentation issue.
Refs #9244.  Modification according to code review.

1. Remove a do-nothing "else if" line 833;
2. Enable 'create' to check whether the series is sorted;
Merge branch 'feature/9244_timeseries_sort' into develop