Support additional collaborators

[chrahunt]

Some of the code and infrastructure need to be reorganized to support collaborators and shared ownership, so it is possible to address fixes in a more timely manner. There are a few tasks under this:

• Move CI to GitHub actions, for less overhead setup and ownership/permission management - done in Add GitHub Actions, drop Travis CI #263
• Move repository to GitHub organization, for easier management of collaborators
• Use separate account for managing Chrome Web Store artifact (suggested here: "we suggest using a new email account just for publishing your Chrome Web Store items" - also good because an account can only ever create 1 Chrome Web Store group publisher)
• Transition ownership to group publisher, to support shared and automated publishing workflows without needing access to the root account (reference)
• Move privacy policy and any other Google Drive hosted artifacts to Google account from above, for easier management
• Look into shared access to Mixpanel events