[FL-1371] New LF-RFID app. Second encounter. (#547)

* File worker: file operations helper.
* Notification app: removed yield
* File worker: write operations, calls to system file widgets
* App ibutton: use file worker
* Lfrfid: generic key loading, add path helper and hex conversion to lib
* FileWorker: plain C verison
* FileWorker: add to lib.mk
* FileWorker: add to C sources, instead of CPP
* Lfrfid: save scene
* App lfrfid: add key scene, saved key menu
* App lfrfid: saved key info scene
* App lfrfid: delete key scene

lib/args/args.h

@@ -46,15 +46,6 @@ size_t args_get_first_word_length(string_t args);
  */
 size_t args_length(string_t args);
 
-/**
- * @brief Convert ASCII hex value to nibble 
- * 
- * @param c ASCII character
- * @param nibble nibble pointer, output
- * @return bool conversion status
- */
-bool args_char_to_hex_nibble(char c, uint8_t* nibble);
-
 /**
  * @brief Convert ASCII hex values to byte
  *