Update copyright headers in generated kernels.

Update copyright headers in generated kernel files to the new format.
Update also some copyright years.

Adjust the generating scripts to reuse the copyright header from
admin/copyright.py to keep it up-to-date.  For the Verlet kernels, some
changes may be required if/when we want to add a copyright header also
into the .pre files.

Part of #818.

Change-Id: I6b5060f12a3c469d0080c73bc9d674e074ce44a4