Document data variables

[esmeetewinkel]

Document data variables stored in the postgres database, for instance in a markdown table in the repo. This includes

app_launch_history: (array of timestamps) list of timestamps of all app launches
first_launch_app_version: (string) app code version on first launch
first_launch_content_version: (string) app content version on first launch
first_launch_ts: (timestamp) timestamp of first app launch
terms_v[date]_accepted: (boolean) user accepted the terms and conditions of [date]
user_mode: (boolean) user is accessing the app as a user (as opposed to as a developer)