Add licenses for tests and test data

- Add license headers to source files (years based on commit dates)
  in `src/test` as well as `qa`
- Add `README.md` to `src/test/data` specifying MIT license

Fixes #3848

src/test/script_tests.cpp

@@ -1,3 +1,7 @@
+// Copyright (c) 2011-2013 The Bitcoin Core developers
+// Distributed under the MIT/X11 software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
 #include "script.h"
 
 #include "data/script_invalid.json.h"