add topic sorting & js to support it

data/static/css/style.css

@@ -859,6 +859,53 @@ a.mention {
   }
 }
 
+ol.sortable-list {
+  display: flex;
+  gap: var(--base-padding);
+  flex-direction: column;
+  list-style: none;
+  flex-grow: 1;
+  margin: 0;
+  padding-left: 0;
+
+  li {
+    display: flex;
+    gap: var(--big-padding);
+  }
+
+  li.immovable .dragger {
+    cursor: not-allowed;
+  }
+}
+
+.plank.dragger {
+  display: flex;
+  align-items: center;
+  /*background-color: var(--bg-color-tertiary);*/
+  padding: var(--base-padding);
+  cursor: move;
+}
+
+.sortable-item-inner {
+  display: flex;
+  gap: var(--base-padding);
+  flex-grow: 1;
+  flex-direction: column;
+
+  & > * {
+    flex-grow: 1;
+  }
+
+  &.row {
+    flex-direction: row;
+  }
+
+  &:not(.row) > * {
+    margin-right: auto;
+  }
+}
+
+
 @media (max-width: 768px) {
   body {
     margin-left: 0;