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/RunGui.hpp

@@ -3,8 +3,12 @@
 class QApplication;
 
 namespace chatterino {
+
+class Args;
 class Paths;
 class Settings;
 
-void runGui(QApplication &a, Paths &paths, Settings &settings);
+void runGui(QApplication &a, Paths &paths, Settings &settings,
+            const Args &args);
+
 }  // namespace chatterino