Add responsive panels to the single-column layout (#10820)

* Add responsive panels to the single-column layout

* Fixes

* Fix not being able to save the preference

* Fix code style issues

* Set max-height on the compose textarea and add a link to relationship manager

app/javascript/mastodon/features/ui/util/async-components.js

@@ -129,3 +129,7 @@ export function ListEditor () {
 export function ListAdder () {
   return import(/*webpackChunkName: "features/list_adder" */'../../list_adder');
 }
+
+export function Search () {
+  return import(/*webpackChunkName: "features/search" */'../../search');
+}