PLT-6282 Make post list stay visible when post textbox height changes (#6323)

* PLT-6282 Changed post drafts to use an action when being stored

* PLT-6282 Triggered post list to update scroll position when post draft changes

* PLT-6282 Changed SuggestionBox to complete suggestions without an event

webapp/actions/post_actions.jsx

@@ -499,3 +499,11 @@ export function performSearch(terms, isMentionSearch, success, error) {
         }
     );
 }
+
+export function storePostDraft(channelId, draft) {
+    AppDispatcher.handleViewAction({
+        type: ActionTypes.POST_DRAFT_CHANGED,
+        channelId,
+        draft
+    });
+}