dnn: move module from opencv_contrib

https://github.com/opencv/opencv_contrib/tree/e6f63c7a38ca40c5dc33e38736e3027e3528d6cb/modules/dnn

modules/dnn/test/test_main.cpp

@@ -0,0 +1,20 @@
+#include "test_precomp.hpp"
+
+static const char* extraTestDataPath =
+#ifdef WINRT
+        NULL;
+#else
+        getenv("OPENCV_DNN_TEST_DATA_PATH");
+#endif
+
+CV_TEST_MAIN("",
+    extraTestDataPath ? (void)cvtest::addDataSearchPath(extraTestDataPath) : (void)0
+)
+
+namespace cvtest
+{
+
+using namespace cv;
+using namespace cv::dnn;
+
+}