Collaborative live position

[cdauth]

Add some sort of live position tracking.

Use cases:

• One person or a few people want to share their locations with the public (a live travel blog)
• One person or a few selected people want to keep track of one or more GPS tracking devices (tracking a vehicle or a pet)
• A lot of people want to see each other’s locations (Critical Maps)

Features:

• When a map is opened through a writable/admin link, add an option to enable showing their current position. This will show a temporary marker on the map for everyone.
  • Optionally, the marker stays (with a different style) when the user stops sharing their position.
  • The user needs to have a way to remove their last location if it's kept on the map
• In the map settings, the location share feature can be configured:
  • Disallow location sharing, allow location sharing, share location automatically
  • Keep/discard locations when users stop sharing
• Introduce some kind of unique secret identifier per user+map that allows users to reclaim a position marker when reopening the map. On the user side, the identifier can be stored in local storage. On the server side, in can be stored in the database but never shared with other users.