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

qa/pull-tester/build-tests.sh.in

@@ -1,4 +1,8 @@
 #!/bin/bash
+# Copyright (c) 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.
+#
 # Param1: The prefix to mingw staging
 # Param2: Path to java comparison tool
 # Param3: Number of make jobs. Defaults to 1.