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/dialogs/LastRunCrashDialog.hpp

@@ -4,10 +4,12 @@
 
 namespace chatterino {
 
+class Args;
+
 class LastRunCrashDialog : public QDialog
 {
 public:
-    LastRunCrashDialog();
+    explicit LastRunCrashDialog(const Args &args);
 };
 
 }  // namespace chatterino