- adds bundlesize package and travis config to run it on pulls (reports size as a check on pulls)
- reconfigure travis configuration so that jobs are split by task for easier review/reporting
- Fix failing phpunit tests exposed as a result of the travis reconfiguration
- Fix legit fail exposed by failing phpunit test in products REST endpoint (permissions related)
- Don't abort plugin initialization when detecting no build asset file but still throw notice (necessary to ensure php tests run in travis because we don't build js/css assets unnecessarily for those tests)