[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/path.c

@@ -0,0 +1,20 @@
+#include "path.h"
+
+void path_extract_filename_no_ext(const char* path, string_t filename) {
+    string_set(filename, path);
+
+    size_t start_position = string_search_rchar(filename, '/');
+    size_t end_position = string_search_rchar(filename, '.');
+
+    if(start_position == STRING_FAILURE) {
+        start_position = 0;
+    } else {
+        start_position += 1;
+    }
+
+    if(end_position == STRING_FAILURE) {
+        end_position = string_size(filename);
+    }
+
+    string_mid(filename, start_position, end_position - start_position);
+}