[GM] adding S3 support for document upload. Again
[GM] Use S3 lib suitable for GAE, that's in maven central
[GM] Created new buckets
[GM] S3 upload seems to be working
[GM] adding download URL
Make file upload pages retain previously uploaded filenames

This allows users who have previously uploaded a file for a question to continue through the page flow without re-uploading the file.

 Also removed some logging.
Document object handling in database

Document objects are created and saved in Pages for pages with document uploads.
Delete document objects from datastore when service is deleted

We don't want orphaned document objects hanging round if a service is deleted, so this deletes them.
Add S3 bucket names

We now have the S3 account set up - these are the buckets in the new account.
Merge pull request #132 from alphagov/use-s3-simple

Use s3 simple