Image upload URls are returned in JSON {"url": "https://someuploadurl"} and failed moment writing is ignored.
Return error when moment fails to write
UploadUrl is moved to a new public model class so that it can be reused.
Add UploadUrl file.
Log severe error for failed moment write, return success to client for photo upload.
Merge pull request #11 from cartland/master

Image upload URLs returned in JSON and ignore failed moments