[FL-1300] iButton app: save selected menu item and selected file position. (#489)

* GUI module submenu: fix documentation
* GUI module submenu: add submenu_set_selected_item fn
* App iButton: use submenu_set_selected_item to store and set selected item in submenu
* App iButton: swap write and emulate in "saved key menu" scene
* App iButton: file select can now switch to the previous selected file
* App iButton: swap write and emulate indexes in "saved key menu" scene

Co-authored-by: あく <alleteam@gmail.com>

lib/common-api/sd-card-api.h

@@ -14,7 +14,8 @@ typedef struct {
         const char* path,
         const char* extension,
         char* result,
-        uint8_t result_size);
+        uint8_t result_size,
+        char* selected_filename);
     void (*check_error)(SdApp* context);
 } SdCard_Api;