resolveUrls->storeUrls
revert CompactControlReadability for easier merging, but definitively think it should be false!
Derive storage path from content directly.
IO: compute md digest from stream
PathFun: create path from content header with fallback to sha-1 hash
GroupManager: resolveStoreUrls returns a future
ResolveArtifacts: will hold the resulting path with the URL
ResolveArtifactsActor: takes advantage of the specified path
ModelValidation: handle specific http, but allow others as well