Port all apps to GApplication.

LibGUI/GApplication.cpp

@@ -2,8 +2,18 @@
 #include <LibGUI/GEventLoop.h>
 #include <LibGUI/GMenuBar.h>
 
+static GApplication* s_the;
+
+GApplication& GApplication::the()
+{
+    ASSERT(s_the);
+    return *s_the;
+}
+
 GApplication::GApplication(int argc, char** argv)
 {
+    ASSERT(!s_the);
+    s_the = this;
     m_event_loop = make<GEventLoop>();
 }
 
@@ -16,6 +26,11 @@ int GApplication::exec()
     return m_event_loop->exec();
 }
 
+void GApplication::exit(int exit_code)
+{
+    m_event_loop->exit(exit_code);
+}
+
 void GApplication::set_menubar(OwnPtr<GMenuBar>&& menubar)
 {
     m_menubar = move(menubar);