Split FilePath into DirPath and FilePath

Sorry I didn't realise that. I am not sure that is a great idea though, because there are more general scenarios than our current one we you need the bucket name to configure S3 things. Maybe this is ok for us for now, but longer term I think we should use bucket / key, because if you wanted to turn this into a signed http request for example (which we would for publishing reports to customers) then the bucket is the server and the key is the http path.