Remove all using directives for STL namespace and members

Made all STL usages explicit to be able automatically find all usages of
particular class or function.

samples/cpp/tutorial_code/ImgTrans/HoughCircle_Demo.cpp

@@ -9,6 +9,7 @@
 #include <iostream>
 #include <stdio.h>
 
+using namespace std;
 using namespace cv;
 
 /**

samples/cpp/tutorial_code/features2D/SURF_FlannMatcher.cpp

@@ -11,6 +11,7 @@
 #include "opencv2/highgui/highgui.hpp"
 #include "opencv2/nonfree/features2d.hpp"
 
+using namespace std;
 using namespace cv;
 
 void readme();

samples/cpp/tutorial_code/features2D/SURF_Homography.cpp

@@ -12,6 +12,7 @@
 #include "opencv2/calib3d/calib3d.hpp"
 #include "opencv2/nonfree/features2d.hpp"
 
+using namespace std;
 using namespace cv;
 
 void readme();

samples/cpp/tutorial_code/objectDetection/objectDetection.cpp

@@ -18,8 +18,8 @@ void detectAndDisplay( Mat frame );
 
 /** Global variables */
 //-- Note, either copy these two files from opencv/data/haarscascades to your current folder, or change these locations
-String face_cascade_name = "haarcascade_frontalface_alt.xml";
-String eyes_cascade_name = "haarcascade_eye_tree_eyeglasses.xml";
+string face_cascade_name = "haarcascade_frontalface_alt.xml";
+string eyes_cascade_name = "haarcascade_eye_tree_eyeglasses.xml";
 CascadeClassifier face_cascade;
 CascadeClassifier eyes_cascade;
 string window_name = "Capture - Face detection";

samples/cpp/tutorial_code/objectDetection/objectDetection2.cpp

@@ -17,8 +17,8 @@ using namespace cv;
 void detectAndDisplay( Mat frame );
 
 /** Global variables */
-String face_cascade_name = "lbpcascade_frontalface.xml";
-String eyes_cascade_name = "haarcascade_eye_tree_eyeglasses.xml";
+string face_cascade_name = "lbpcascade_frontalface.xml";
+string eyes_cascade_name = "haarcascade_eye_tree_eyeglasses.xml";
 CascadeClassifier face_cascade;
 CascadeClassifier eyes_cascade;
 string window_name = "Capture - Face detection";