Add a default/dummy bounding box on site setup

[c-w]

For more background on this change, please refer to the discussion in #233

@Smarker: Do you see any concerns for this change from an admin/editing perspective? It should be possible to edit the dummy bounding box after the deployment is finished, right?

@erikschlegel: Any objections to this change?

[Smarker]

This change looks good. A small change on the UI would be needed, so that you can edit the bbox. I don't think any service change would be necessary.

It seems like we'd need to add an input field for geofence/bounding box, since I don't think this is editable via admin sitesettings. I think it would just be a matter of adding another input field like the one here

We already have the bbox value saved here.

When you save site settings, save_settings will be called, which calls editSite. EditSite can already change this bbox value.

[Smarker]

LGTM - we would need to edit the admin sitesettings react component and add an input field, so that the user can edit the bbox.