add editing capabilities

[dgraf-gh]

there needs to be a way to edit/add/delete the polygon of a place

• what happens if the new polygon spans multiple places? They need to be merged and all references should be adjusted.

[dgraf-gh]

• create a new page
• this will be linked from the timeline and also from Settings > Places
• there:
  • a user can change properties of a place
  • including adding/removing a polygon
  • when pressing save, the user should be presented with a list what will happen.
    • existing places can be dropped because the new polygon will cover this
    • trips need to be adjusted then