dateutils: strftime improvement
- Adds a new function strftime to dateutils to use instead of Python stdlib datetime in order to support before 1900. (closes #1065)
- Adds tests for improved strftime function.
- Changes standard strftime function or adds exception handling in bibsort, bibauthorid, bibcirculation and websearch.
Reviewed-by: Jan Aage Lavik <jan.age.lavik@cern.ch>
Tested-by: Tibor Simko <tibor.simko@cern.ch>