Gaufrette metadata support

I had a problem where a file that was being uploaded to Amazon S3 wasn't getting the correct mime type set on S3, this meant that it wasn't being displayed on the website correctly.

This fix will check to see if the adapter is a metadata supporter and if so, will set the metadata with the content type (mime type).

I have added tests to cover the scenario where the user may be using a metadata supported adapter and where they are not.

I also altered the doctrine mongodb dependency to 1.0.*@dev which should resolve the composer issues breaking the build and was required to get my tests to run.