ts: refactor OpenCV tests

- removed tr1 usage (dropped in C++17)
- moved includes of vector/map/iostream/limits into ts.hpp
- require opencv_test + anonymous namespace (added compile check)
- fixed norm() usage (must be from cvtest::norm for checks) and other conflict functions
- added missing license headers

modules/imgcodecs/test/test_webp.cpp

@@ -1,8 +1,9 @@
+// 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 "test_precomp.hpp"
 
-using namespace cv;
-using namespace std;
-using namespace std::tr1;
+namespace opencv_test { namespace {
 
 #ifdef HAVE_WEBP
 
@@ -104,3 +105,5 @@ TEST(Imgcodecs_WebP, encode_decode_with_alpha_webp)
 }
 
 #endif // HAVE_WEBP
+
+}} // namespace