Extract MakeUnique into utilmemory.h

And use it to reduce chainparamsbase's direct reliance on util.h to
only args handling.

utilmemory.h can be replaced with <memory> once we move to C++14.

src/interfaces/handler.cpp

@@ -4,7 +4,7 @@
 
 #include <interfaces/handler.h>
 
-#include <util.h>
+#include <utilmemory.h>
 
 #include <boost/signals2/connection.hpp>
 #include <utility>