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/pull-tester.sh

@@ -1,4 +1,8 @@
 #!/bin/sh
+# 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.
+#
 # Helper script for pull-tester.
 #Param 1: path to bitcoin srcroot
 #Param ...: arguments for build-test.sh