Adding OWNERS files

(bcc www-style.)

About two weeks ago I opened a bunch of PRs for web-platform-tests adding
missing OWNERS files. Tomorrow (Thursday) I intend to go through the PRs,
remove non-responders, and merge. Please review (ideally with GitHub's
review feature) if you are OK with being added to OWNERS. It means you’ll
get notified any time someone submits a PR. And the tests could only be
merged to the master branch after review from one of the OWNERS.

https://github.com/w3c/web-platform-tests/issues/5915#issuecomment-389447585

If you read this after a PR has been merged but want to be in OWNERS,
please open a new PR.

cheers,
-- 
Simon Pieters
Bocoup https://bocoup.com/