Release 2.0.26 (#4087)

- setting "rounding days" not required
- developer: added user pref for public holiday group (to be used by plugins)
- developer: added WorkingTimeYearEvent (to be used by plugins)
- user pref: cleanup work contract form and support more fields (to be used by plugins)
- code cleanup
- bump theme and composer packages

src/Controller/SystemConfigurationController.php

@@ -422,6 +422,7 @@ final class SystemConfigurationController extends AbstractController
                         ]),
                     (new Configuration('timesheet.rounding.default.days'))
                         ->setType(WeekDaysType::class)
+                        ->setRequired(false)
                         ->setTranslationDomain('system-configuration'),
                 ]),
             (new SystemConfigurationModel('invoice'))