[Feature request] Manually set position for saved contacts

[spunip6969]

It would great to manually set (or override) the position for a saved contact.

• Contacts that don't broadcast their position can be displayed on the map.
• Nodes you manage personally could have a public approximate location, and an exact position locally.
• You could also manually null a contact's position if you wish to remove them from the local map.

This could work similarly to the existing "Rename contact" field.

Thanks :)