Bug 8365: Add unit tests and fix QA issues

Bug 8365: Add unit tests and fix QA issues

This patch adds some unit tests for CalcDateDue and GetLoanLength

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
All tests and QA script pass.

Tests done:
- Checked update works correctly for existing circulation rules.
- Adding, deleting and overwriting circulation rules works.
- Renewals work for different circulation rules and changes
  to the holiday calendar.
Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>