LibGUI: Rename GEventLoop::exit() and GApplication::exit() to quit().

These functions don't exit immediately, but rather on the next iteration
of the event loop.

Since exit() is already used by the standard library, let's call it quit()
instead. That way, saying exit() means the same thing here as anywhere else.

LibGUI/GEventLoop.cpp

@@ -66,7 +66,7 @@ GEventLoop& GEventLoop::main()
     return *s_mainGEventLoop;
 }
 
-void GEventLoop::exit(int code)
+void GEventLoop::quit(int code)
 {
     m_exit_requested = true;
     m_exit_code = code;
@@ -257,7 +257,7 @@ void GEventLoop::wait_for_event()
         if (event.type == WSAPI_ServerMessage::Error) {
             dbgprintf("GEventLoop got error message from server\n");
             dbgprintf("  - error message: %s\n", String(event.text, event.text_length).characters());
-            exit(1);
+            quit(1);
             return;
         }
 
@@ -307,7 +307,7 @@ bool GEventLoop::drain_messages_from_server()
         ssize_t nread = read(m_event_fd, &message, sizeof(WSAPI_ServerMessage));
         if (nread < 0) {
             perror("read");
-            exit(1);
+            quit(1);
             return false;
         }
         if (nread == 0)