src: Reorganizing source code in preparation to merge NRD code

Note that as of this commit, there are several changes in location of
compiled binaries in `build/` folder:

* `nfd` has been moved to `build/bin/nfd`
* `unit-tests` has been split into `unit-tests-core` and `unit-tests-daemon`

Change-Id: I2c830c117879edbaa5457d6423c13f0273285919
Refs: #1486
diff --git a/tests/core/version.cpp b/tests/core/version.cpp
index ee29615..669a866 100644
--- a/tests/core/version.cpp
+++ b/tests/core/version.cpp
@@ -22,7 +22,7 @@
  * NFD, e.g., in COPYING.md file.  If not, see <http://www.gnu.org/licenses/>.
  **/
 
-#include "core/version.hpp"
+#include "version.hpp"
 #include "core/logger.hpp"
 
 #include "tests/test-common.hpp"