Investigation into a solution for seeing a history of changes across a site in one place.

Description of problem: Sometimes queries from Legal Dept. that we can't answer to (e.g. was this company ever explicitly mentioned in the post?) - with the current reporting, we can't answer this Q, because there are elements we can't see now . Consider an "Activity log" to help admins.

Example list of activities to track:

• changes to title, permalink, SEO fields, and other content that isn't tracked in a post's revision history
• changes to settings

Perhaps https://wordpress.org/plugins/aryo-activity-log ? or something similar.

Tasks

• Investigate feasibility of exposing activity logs of things already saved in WP database (eg. revisions)
• Check if keeping less revisions would affect this. See PLANET-5727
• Ideally Activity log should contain meaningful changes (eg. not autosaves or previews)