added functionality to add / remove labels from comments

frontend/@types/v-clipboard/index.d.ts

frontend/package.json

frontend/src/api.ts

frontend/src/components/BaseLayout.vue

frontend/src/components/feedback_labels/FeedbackLabel.vue

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

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

...end/src/components/feedback_labels/FeedbackLabelsList.vue

frontend/src/components/feedback_labels/LabelSelector.vue

.../src/components/submission_notes/SubmissionCorrection.vue

...tend/src/components/submission_notes/base/CommentForm.vue

.../src/components/submission_notes/base/FeedbackComment.vue

...s/submission_notes/toolbars/AnnotatedSubmissionLabels.vue

frontend/src/models.ts

frontend/src/store/modules/feedback-labels.ts

frontend/src/store/modules/submission-notes.ts

frontend/yarn.lock