refactor: Twitch PubSub client (#5059)

* Remove unused `setAccountData` function

* Move PubSub out of TwitchIrcServer and into Application

* Add changelog entry

* fix: assert feedback

* Add PubSub::unlistenPrefix as per review suggestion

* Fix tests

* quit pubsub on exit

might conflict with exit removal, so can be reverted but this shows it's possible

* Don't manually call stop on clients, it's called when the connection is closed

* nit: rename `mainThread` to `thread`

* Join in a thread!!!!!!!!

src/RunGui.cpp

@@ -288,6 +288,8 @@ void runGui(QApplication &a, Paths &paths, Settings &settings, const Args &args)
     flushClipboard();
 #endif
 
+    app.fakeDtor();
+
     _exit(0);
 }
 }  // namespace chatterino