Add option for username tab completion only with an @ prefix (#1573)

* add an additional check for username completion without an @ prefix

* Changed setting name

* default userCompletionOnlyWithAt to false

src/singletons/Settings.hpp

@@ -134,6 +134,8 @@ public:
         "/behaviour/autocompletion/smallStreamerLimit", 1000};
     BoolSetting prefixOnlyEmoteCompletion = {
         "/behaviour/autocompletion/prefixOnlyCompletion", true};
+    BoolSetting userCompletionOnlyWithAt = {
+        "/behaviour/autocompletion/userCompletionOnlyWithAt", false};
 
     FloatSetting pauseOnHoverDuration = {"/behaviour/pauseOnHoverDuration", 0};
     EnumSetting<Qt::KeyboardModifier> pauseChatModifier = {