Subghz app example (#365)

* Gui: ported submenu and view_dispatcher_remove_view from iButton branch

* App gui-test: use backported submenu api

* App subghz: initial commit

* App subghz: syntax fix

* App gui-test: fix submenu callback

* App subghz: add subfolders to build

* Gui view: c++ verison of with_view_model

* Subghz app: simple spectrum settings view

* Subghz app: add spectrum settings view to view manager

* Subghz app: spectrum settings scene

Co-authored-by: coreglitch <mail@s3f.ru>

applications/subghz/subghz-event.h

@@ -0,0 +1,21 @@
+#pragma once
+#include <stdint.h>
+
+class SubghzEvent {
+public:
+    // events enum
+    enum class Type : uint8_t {
+        Tick,
+        Back,
+        MenuSelected,
+        NextScene,
+    };
+
+    // payload
+    union {
+        uint32_t menu_index;
+    } payload;
+
+    // event type
+    Type type;
+};