Taskbar: Add a quick launch bar

This is a tiny bar at the left of the taskbar where you can put
your most used apps to launch them with a single click. In a way,
it's another replacement for the Launcher, in addition to the app
menu. Unlike the launcher and the menu, it's not meant to be the
primary way to launch apps; it's only a faster way to launch a few
most often used utilities.

Applications/Taskbar/main.cpp

@@ -1,10 +1,17 @@
 #include "TaskbarWindow.h"
 #include <LibGUI/GApplication.h>
+#include <signal.h>
 
 int main(int argc, char** argv)
 {
     GApplication app(argc, argv);
     TaskbarWindow window;
     window.show();
+
+    signal(SIGCHLD, [](int signo) {
+        (void)signo;
+        wait(nullptr);
+    });
+
     return app.exec();
 }