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/view/subghz-view-spectrum-settings.h

@@ -0,0 +1,25 @@
+#include <gui/view.h>
+
+class SubghzViewSpectrumSettings {
+public:
+    SubghzViewSpectrumSettings();
+    ~SubghzViewSpectrumSettings();
+
+    View* get_view();
+
+    // ok callback methods
+    typedef void (*OkCallback)(void* context);
+    void set_ok_callback(OkCallback callback, void* context);
+    void call_ok_callback();
+
+    // model data getters/setters
+    void set_start_freq(uint32_t start_freq);
+    uint32_t get_start_freq();
+
+private:
+    View* view;
+
+    // ok callback data
+    OkCallback ok_callback = nullptr;
+    void* ok_callback_context = nullptr;
+};