Show all courses per default in timetable management

aleksis/apps/lesrooster/frontend/components/timetable_management/TimetableManagement.vue

@@ -1057,7 +1057,7 @@ export default defineComponent({
             <v-data-iterator
               :items="selectableCourses"
               item-key="key"
-              :items-per-page="12"
+              :items-per-page="-1"
               single-expand
               :search="courseSearch"
               sort-by="data.lessonRatio"