[FL-1329] Settings (#563)

* Menu: secondary menu rendering
* Manu: reset window position on enter to new menu
* App-loader: settings menu
* Applications: add settings app list
* App backlight-control: all work related to turning off the display is now in the notification app
* App notification: settings save and load
* Gui: variable item list module
* App: new notification settings app
* Display: backlight is now fully serviced in the notification app
* Gui: update variable item list module documentation

applications/gui/modules/variable-item-list.h

@@ -0,0 +1,64 @@
+#pragma once
+#include <gui/view.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+typedef struct VariableItemList VariableItemList;
+typedef struct VariableItem VariableItem;
+typedef void (*VariableItemChangeCallback)(VariableItem* item);
+
+/** Allocate and initialize VariableItemList
+ * @return VariableItemList* 
+ */
+VariableItemList* variable_item_list_alloc();
+
+/** Deinitialize and free VariableItemList
+ * @param variable_item_list VariableItemList instance
+ */
+void variable_item_list_free(VariableItemList* variable_item_list);
+View* variable_item_list_get_view(VariableItemList* variable_item_list);
+
+/** Add item to VariableItemList
+ * @param variable_item_list VariableItemList instance
+ * @param label item name
+ * @param values_count item values count
+ * @param change_callback called on value change in gui
+ * @param context item context
+ * @return VariableItem* item instance
+ */
+VariableItem* variable_item_list_add(
+    VariableItemList* variable_item_list,
+    const char* label,
+    uint8_t values_count,
+    VariableItemChangeCallback change_callback,
+    void* context);
+
+/** Set item current selected index
+ * @param item VariableItem* instance
+ * @param current_value_index 
+ */
+void variable_item_set_current_value_index(VariableItem* item, uint8_t current_value_index);
+
+/** Set item current selected text
+ * @param item VariableItem* instance
+ * @param current_value_text 
+ */
+void variable_item_set_current_value_text(VariableItem* item, const char* current_value_text);
+
+/** Get item current selected index
+ * @param item VariableItem* instance
+ * @return uint8_t current selected index
+ */
+uint8_t variable_item_get_current_value_index(VariableItem* item);
+
+/** Get item context
+ * @param item VariableItem* instance
+ * @return void* item context
+ */
+void* variable_item_get_context(VariableItem* item);
+
+#ifdef __cplusplus
+}
+#endif