MB-7728: Add copyright headers to all files

This is something that our cpplint tool turns on and it makes
our product look a little bit more profesional. I have also
enabled the tool to begin checking for these headers so it will
start complaining if we add a new file without a copyright header.

Change-Id: Ie956fdf7027bf56d9665ee455acd3c109fcacc76
Reviewed-on: http://review.couchbase.org/24560
Reviewed-by: Chiyoung Seo <chiyoung.seo@gmail.com>
Reviewed-by: Jin Lim <jin@couchbase.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>