Return Key from S3 response

Returning the key is important, when a filename contains Spaces or
other non-url safe characters the ‘Location’ parameter has encoded
them.  When this happens, it’s impossible to use the ‘url’ as the key
when referencing the file via the AWS SDK as a bucket object.

e.g. I upload a file called ‘I have spaces.txt’.  The ‘Location’ in
AWS’s response is ‘https://[bucket].s3.amazonaws.com/I+have+spaces.txt'
If we try to use this url to determine the key, URI.decode leaves the
+’s in there.  The +’s could have been part of the original filename
‘I+have+strings.txt’.

There’s no good way to clean the filename before hand, so, this really
needs to return the key back to the callback url along with the
url/location.
Merge branch 'add-key-to-callback-post'