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/select3dobj.cpp

@@ -17,6 +17,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 
+using namespace std;
 using namespace cv;
 
 const char* helphelp =