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/widgets/settingspages/GeneralPage.cpp

@@ -525,6 +525,8 @@ void GeneralPage::initLayout(SettingsLayout &layout)
     layout.addCheckbox(
         "Only search for emote autocompletion at the start of emote names",
         s.prefixOnlyEmoteCompletion);
+    layout.addCheckbox("Only search for username autocompletion with an @",
+                       s.userCompletionOnlyWithAt);
 
     layout.addCheckbox("Show twitch whispers inline", s.inlineWhispers);
     layout.addCheckbox("Highlight received inline whispers",