Start app menu item for registered apps

OpenKeychain/src/main/res/menu/api_app_settings.xml

@@ -2,6 +2,12 @@
 <menu xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:app="http://schemas.android.com/apk/res-auto">
 
+    <item
+        android:id="@+id/menu_api_settings_start"
+        android:title="@string/api_settings_start"
+        android:icon="@drawable/ic_action_play"
+        app:showAsAction="always" />
+
     <item
         android:id="@+id/menu_api_settings_revoke"
         android:title="@string/api_settings_revoke"