Add stub for jf-live-writer

The goal of this writer is to provide immediate writing
without delay -> following the detector.

jf-live-writer/test/main.cpp

@@ -0,0 +1,8 @@
+#include "gtest/gtest.h"
+
+using namespace std;
+
+int main(int argc, char **argv) {
+  ::testing::InitGoogleTest(&argc, argv);
+  return RUN_ALL_TESTS();
+}