Merge branch 'threecolumn' into shigusegubu-vue3

* threecolumn:
  fixate conversation heading
  fix overflow that sometimes happens in sidebar due to too wide file upload element

src/components/conversation/conversation.vue

@@ -7,7 +7,7 @@
   >
     <div
       v-if="isExpanded"
-      class="panel-heading conversation-heading"
+      class="panel-heading conversation-heading -sticky"
     >
       <span class="title"> {{ $t('timeline.conversation') }} </span>
       <button

src/components/media_upload/media_upload.vue

@@ -19,7 +19,7 @@
       v-if="uploadReady"
       :disabled="disabled"
       type="file"
-      style="position: fixed; top: -100em"
+      style="position: fixed; top: -100em; max-width: 0; max-height: 0"
       multiple="true"
       @change="change"
     >

src/components/timeline/timeline.scss

@@ -27,4 +27,8 @@
   .timeline-footer {
     border: none;
   }
+
+  .conversation-heading {
+    top: calc(var(--panel-heading-height) * 2);
+  }
 }