samples: avoid using of legacy C-like API

- CV_RGB() macro is moved into opencv2/imgproc.hpp from imgproc_c.h
- samples/cpp/filestorage_base64.cpp is dropped

samples/cpp/videowriter_basic.cpp

@@ -35,7 +35,7 @@ int main(int, char**)
 
     //--- INITIALIZE VIDEOWRITER
     VideoWriter writer;
-    int codec = CV_FOURCC('M', 'J', 'P', 'G');  // select desired codec (must be available at runtime)
+    int codec = VideoWriter::fourcc('M', 'J', 'P', 'G');  // select desired codec (must be available at runtime)
     double fps = 25.0;                          // framerate of the created video stream
     string filename = "./live.avi";             // name of the output video file
     writer.open(filename, codec, fps, src.size(), isColor);