refactor: Make Args less of a singleton (#5041)

This means it's no longer a singleton, and its lifetime is bound to our application.
This felt like a good small experiment to see how its changes would look
if we did this.
As a shortcut, `getApp` that is already a mega singleton keeps a
reference to Args, this means places that are a bit more difficult to
inject into call `getApp()->getArgs()` just like other things are
accessed.

src/controllers/plugins/PluginController.cpp

@@ -233,7 +233,7 @@ void PluginController::load(const QFileInfo &index, const QDir &pluginDir,
     auto *temp = plugin.get();
     this->plugins_.insert({pluginName, std::move(plugin)});
 
-    if (getArgs().safeMode)
+    if (getApp()->getArgs().safeMode)
     {
         // This isn't done earlier to ensure the user can disable a misbehaving plugin
         qCWarning(chatterinoLua) << "Skipping loading plugin " << meta.name