UX: Allow claim of topic via posts

assets/javascripts/discourse-assign/connectors/flagged-post-controls/claim-flagged-post.hbs

@@ -1,3 +1 @@
-{{#if actableFilter}}
+{{claim-topic topic=flaggedPost.topic}}
-  {{claim-topic topic=flaggedPost.topic}}
-{{/if}}

assets/javascripts/discourse-assign/connectors/flagged-post-controls/claim-flagged-post.js.es6

@@ -0,0 +1,5 @@
+export default {
+  shouldRender(args) {
+    return args.actableFilter && !args.topic;
+  }
+};