Minor refactoring in several C++ samples:

- bgfg_segm
- peopledetect
- opencv_version
- dnn/colorization
- tapi/opencl_custom_kernel
- tapi/dense_optical_flow (renamed tvl1_optical_flow)

samples/cpp/opencv_version.cpp

@@ -1,16 +1,17 @@
+// This file is part of OpenCV project.
+// It is subject to the license terms in the LICENSE file found in the top-level directory
+// of this distribution and at http://opencv.org/license.html
+
 #include <opencv2/core/utility.hpp>
 #include <iostream>
 
-const char* keys =
-{
-    "{ b build | | print complete build info }"
-    "{ h help  | | print this help           }"
-};
+static const std::string keys = "{ b build | | print complete build info }"
+                                "{ h help  | | print this help           }";
 
 int main(int argc, const char* argv[])
 {
     cv::CommandLineParser parser(argc, argv, keys);
-
+    parser.about("This sample outputs OpenCV version and build configuration.");
     if (parser.has("help"))
     {
         parser.printMessage();
@@ -27,6 +28,5 @@ int main(int argc, const char* argv[])
     {
         std::cout << "Welcome to OpenCV " << CV_VERSION << std::endl;
     }
-
     return 0;
 }