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.

(cherry picked from commit 2a6fb2867e)
(only cherry picked "apps/trancascade")

apps/traincascade/traincascade.cpp

@@ -9,7 +9,7 @@ using namespace std;
 int main( int argc, char* argv[] )
 {
     CvCascadeClassifier classifier;
-    String cascadeDirName, vecName, bgName;
+    string cascadeDirName, vecName, bgName;
     int numPos    = 2000;
     int numNeg    = 1000;
     int numStages = 20;