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/scene/subghz-scene-start.h

@@ -0,0 +1,12 @@
+#pragma once
+#include "subghz-scene-generic.h"
+
+class SubghzSceneStart : public SubghzScene {
+public:
+    void on_enter(SubghzApp* app) final;
+    bool on_event(SubghzApp* app, SubghzEvent* event) final;
+    void on_exit(SubghzApp* app) final;
+
+private:
+    void submenu_callback(void* context, uint32_t index);
+};