[copyright] add MIT license headers to .sh scripts where missing

Years are set according to 'git log' history

contrib/tidy_datadir.sh

@@ -1,4 +1,7 @@
 #!/bin/bash
+# Copyright (c) 2013 The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 if [ -d "$1" ]; then
   cd "$1"