Inspector: Add a GUI tool for viewing a remote process's CObject graph

Here comes the foundation for a neat remote debugging tool.

Right now, it connects to a remote process's CEventLoop RPC socket and
retreives the remote object graph JSON dump. The remote object graph
is then reconstructed and exposed through a GModel subclass, which is
then displayed in a GTreeView.

It's pretty cool, I think. :^)

DevTools/Inspector/main.cpp

@@ -0,0 +1,41 @@
+#include "RemoteObjectGraphModel.h"
+#include <LibGUI/GApplication.h>
+#include <LibGUI/GBoxLayout.h>
+#include <LibGUI/GTreeView.h>
+#include <LibGUI/GWindow.h>
+#include <stdio.h>
+
+[[noreturn]] static void print_usage_and_exit()
+{
+    printf("usage: Inspector <pid>\n");
+    exit(0);
+}
+
+int main(int argc, char** argv)
+{
+    if (argc != 2)
+        print_usage_and_exit();
+
+    bool ok;
+    pid_t pid = String(argv[1]).to_int(ok);
+    if (!ok)
+        print_usage_and_exit();
+
+    GApplication app(argc, argv);
+
+    auto* window = new GWindow;
+    window->set_title("Inspector");
+    window->set_rect(150, 150, 300, 500);
+
+    auto* widget = new GWidget;
+    window->set_main_widget(widget);
+    widget->set_fill_with_background_color(true);
+    widget->set_layout(make<GBoxLayout>(Orientation::Vertical));
+
+    auto* tree_view = new GTreeView(widget);
+    tree_view->set_model(RemoteObjectGraphModel::create_with_pid(pid));
+    tree_view->model()->update();
+
+    window->show();
+    return app.exec();
+}