Fix and update translation (keys)

...ooster/frontend/components/lesson_raster/LessonRaster.vue

...lesrooster/frontend/components/lesson_raster/SlotCard.vue

...esrooster/frontend/components/supervision/Supervision.vue

...s/timebound_course_config/TimeboundCourseConfigRaster.vue

...d/components/timetable_management/TimetableManagement.vue

...s/lesrooster/frontend/components/timetables/Timetable.vue

...rooster/frontend/components/timetables/timetables.graphql

...ontend/components/validity_range/CopyFromTimeGridMenu.vue

aleksis/apps/lesrooster/frontend/messages/de.json

aleksis/apps/lesrooster/frontend/messages/en.json