* feat(street-level): export the KartaView and Panoramax providers
A host that composes Street Level with its own provider list can already
import the Mapillary and Google Street View providers; KartaView and Panoramax
were reachable only through the default list, which needs a Mapillary source.
Exporting them lets a host offer the keyless providers without Mapillary.
* chore: changelog entry for the Street Level provider exports
* feat(street-level): send Mapillary Graph lookups to a source endpoint
A Mapillary source can take a graphEndpoint, a Graph API base that adds
the token itself. Its sequence lookups go there through the source's
transport, and the photo viewer uses MapillaryJS's stock GraphDataProvider
at that endpoint, so a host that proxies Mapillary needs no client token in
the page. Without it, behaviour is unchanged: direct Graph API calls with
the client token.
