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.cpp

@@ -0,0 +1,10 @@
+#include "subghz-app.h"
+
+// app enter function
+extern "C" int32_t app_subghz(void* p) {
+    SubghzApp* app = new SubghzApp();
+    app->run();
+    delete app;
+
+    return 255;
+}