Auto fetch user address coordinates

[LGro]

• [x] whenever any user's profile contact address does not have coordinates associated yet, use the default geo location provider to automatically determine them
• [ ] when no coordinates can be found, display a form so users can enter coordinates manually (potentially along with an explanation text)
• [ ] allow opt-out of automatic coordinate resolution via the settings page

Never fetch the coordinates for the addresses of contacts because this would leak private information without their consent.