flat -> text and round -> rounded in buttons

frontend/src/components/AutoLogout.vue

frontend/src/components/BaseLayout.vue

frontend/src/components/FreeLocksButton.vue

frontend/src/components/InstanceActions.vue

frontend/src/components/PasswordChangeDialog.vue

frontend/src/components/RegisterDialog.vue

frontend/src/components/export/DataExport.vue

frontend/src/components/export/ExportDialog.vue

frontend/src/components/export/InstanceExport.vue

frontend/src/components/student_list/StudentList.vue

...c/components/submission_notes/RouteChangeConfirmation.vue

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

...d/src/components/submission_notes/base/SubmissionLine.vue

...ssion_notes/toolbars/AnnotatedSubmissionBottomToolbar.vue

...bmission_notes/toolbars/AnnotatedSubmissionTopToolbar.vue

...mission_notes/toolbars/ToggleFeedbackVisibilityButton.vue

frontend/src/components/submission_type/SubmissionType.vue

...tend/src/components/submission_type/solution/Solution.vue

...c/components/submission_type/solution/SolutionComment.vue