Assign OSM users to specific areas

[smit1678]

From feedback: Add a list of OSM editors (similar to how managers are added). These editors can be assigned task areas. They can mark the completion status of their task.

This should be thought through some more on how we would implement and manage this. Some areas have individual users overseeing that area, some have teams of users.

[Dragneel7]

@smit1678 Is this similar to the issue #306 where users will be assigned a sub area of the campaign and will be linked to that part of the map.