Create window

src/main.cpp

@@ -1,4 +1,16 @@
+module;
+#include <gtkmm.h>
 export module xmpp_client.main;
 import xmpp_client.library;
 
-auto main() -> int {};
+struct MainWindow : public Gtk::Window {
+  MainWindow() {
+    this->set_title("XMPP Client");
+    this->set_default_size(200, 200);
+  };
+};
+
+auto main(int argc, char* argv[]) -> int {
+  auto app = Gtk::Application::create("org.xmpp_client.xmpp_client");
+  return app->make_window_and_run<MainWindow>(argc, argv);
+};