Attachment list for uncached attachments (#2110)

* For undownloaded attachments, set type :unknown, display them as a list in the web UI

* Fix case when attachment type is set explicitly

app/assets/stylesheets/components.scss

@@ -2346,3 +2346,53 @@ button.icon-button.active i.fa-retweet {
     }
   }
 }
+
+.attachment-list {
+  display: flex;
+  font-size: 14px;
+  border: 1px solid lighten($color1, 8%);
+  border-radius: 4px;
+  margin-top: 14px;
+  overflow: hidden;
+}
+
+.attachment-list__icon {
+  flex: 0 0 auto;
+  color: lighten($color1, 26%);
+  padding: 8px 18px;
+  cursor: default;
+  border-right: 1px solid lighten($color1, 8%);
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  justify-content: center;
+  font-size: 26px;
+
+  .fa {
+    display: block;
+  }
+}
+
+.attachment-list__list {
+  list-style: none;
+  padding: 4px 0;
+  padding-left: 8px;
+  display: flex;
+  flex-direction: column;
+  justify-content: center;
+
+  li {
+    display: block;
+    padding: 4px 0;
+  }
+
+  a {
+    text-decoration: none;
+    color: lighten($color1, 26%);
+    font-weight: 500;
+
+    &:hover {
+      text-decoration: underline;
+    }
+  }
+}