added documentation for most components and did some smaller refactorings

frontend/src/components/export/DataExport.vue

frontend/src/components/export/InstanceExport.vue

frontend/src/components/export/README.md

...tend/src/components/feedback_labels/FeedbackLabelForm.vue

frontend/src/components/feedback_labels/FeedbackLabelTab.vue

...d/src/components/feedback_labels/FeedbackLabelUpdater.vue

frontend/src/components/feedback_labels/LabelSelector.vue

frontend/src/components/feedback_labels/README.md

...end/src/components/feedback_list/FeedbackListHelpCard.vue

...nd/src/components/feedback_list/FeedbackSearchOptions.vue

frontend/src/components/feedback_list/FeedbackTable.vue

frontend/src/components/feedback_list/README.md

frontend/src/components/instance_config/ConfigDialog.vue

frontend/src/components/instance_config/README.md

frontend/src/components/mixins/README.md

frontend/src/components/mixins/commentLabelSelector.ts

frontend/src/components/mixins/exportMixin.ts

frontend/src/components/student/README.md

frontend/src/components/student_list/README.md

frontend/src/components/student_list/StudentList.vue