Move "clapper_src" dir to "src"

The "clapper_src" directory name was unusual. This was done to make it work as a widget for other apps. Now that this functionality got removed it can be named simply "src" as recommended by guidelines.

src/main.js

@@ -0,0 +1,12 @@
+imports.gi.versions.Gdk = '4.0';
+imports.gi.versions.Gtk = '4.0';
+
+const { Gst } = imports.gi;
+const { App } = imports.src.app;
+
+Gst.init(null);
+
+function main(argv)
+{
+    new App().run(argv);
+}