Integrate google streetview
The goal of this issue is to add Google Streetview as a source of streetview imagery on the map. This is quite a big project with at least the following individual tasks.
- adding google streetview markers (maybe blue?) to the map
- adding the google streetview JS plugin as a popup over the map (similar to the Mapillary one)
- enabling links to google streetview images within features and flags (similar to the current Mapillary intergration)