[FL-1885] USB-UART bridge (#778)

* [FL-1885] USB-UART: app and worker
* [FL-1885] USB-UART: UART on CDC0

Co-authored-by: Aleksandr Kutuzov <alleteam@gmail.com>

applications/gpio/gpio_app_i.h

@@ -7,8 +7,8 @@
 #include <gui/gui.h>
 #include <gui/view_dispatcher.h>
 #include <gui/scene_manager.h>
+#include <gui/modules/submenu.h>
 #include <notification/notification-messages.h>
-
 #include <gui/modules/variable-item-list.h>
 #include "views/gpio_test.h"
 
@@ -25,4 +25,5 @@ struct GpioApp {
 typedef enum {
     GpioAppViewVarItemList,
     GpioAppViewGpioTest,
+    GpioAppViewUsbUart,
 } GpioAppView;