PaintBrush: Start working on a simple painting application.

Applications/PaintBrush/main.cpp

@@ -0,0 +1,18 @@
+#include "PaintableWidget.h"
+#include <LibGUI/GApplication.h>
+#include <LibGUI/GWindow.h>
+
+int main(int argc, char** argv)
+{
+    GApplication app(argc, argv);
+
+    auto* window = new GWindow;
+    window->set_title("PaintBrush");
+    window->set_rect(100, 100, 600, 400);
+
+    auto* paintable_widget = new PaintableWidget(nullptr);
+    window->set_main_widget(paintable_widget);
+
+    window->show();
+    return app.exec();
+}