Update copyright headers.

- Add copyright headers to files that did not already have them
- Update the year to the last year the file was modified in files with
  existing headers.

wa/framework/exception.py

@@ -1,4 +1,4 @@
-#    Copyright 2013-2015 ARM Limited
+#    Copyright 2013-2018 ARM Limited
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.