Add constants for app features

src/components/subtitleeditor/subtitleeditor.js

@@ -1,4 +1,6 @@
 import escapeHtml from 'escape-html';
+
+import { AppFeature } from 'constants/appFeature';
 import { appHost } from '../apphost';
 import dialogHelper from '../dialogHelper/dialogHelper';
 import layoutManager from '../layoutManager';
@@ -440,7 +442,7 @@ function showEditorInternal(itemId, serverId) {
         }
 
         // Don't allow redirection to other websites from the TV layout
-        if (layoutManager.tv || !appHost.supports('externallinks')) {
+        if (layoutManager.tv || !appHost.supports(AppFeature.ExternalLinks)) {
             dlg.querySelector('.btnHelp').remove();
         }