Fix home regeneration (#6251)

* Fix regeneration marker not being removed after completion

* Return HTTP 206 from /api/v1/timelines/home if regeneration in progress
Prioritize RegenerationWorker by putting it into default queue

* Display loading indicator and poll home timeline while it regenerates

* Add graphic to regeneration message

* Make "not found" indicator consistent with home regeneration

app/javascript/mastodon/features/list_timeline/index.js

@@ -120,13 +120,17 @@ export default class ListTimeline extends React.PureComponent {
     if (typeof list === 'undefined') {
       return (
         <Column>
-          <LoadingIndicator />
+          <div className='scrollable'>
+            <LoadingIndicator />
+          </div>
         </Column>
       );
     } else if (list === false) {
       return (
         <Column>
-          <MissingIndicator />
+          <div className='scrollable'>
+            <MissingIndicator />
+          </div>
         </Column>
       );
     }