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/widgets/Window.cpp

@@ -737,7 +737,7 @@ void Window::onAccountSelected()
     }
 #endif
 
-    if (getArgs().safeMode)
+    if (getApp()->getArgs().safeMode)
     {
         windowTitle += " (safe mode)";
     }