Be resilient to file store errors

[MarshallOfSound]

Currently if an unhandled error occurs while transferring files from a TemporaryFile to a released File the operation is aborted but not cleaned up. This means the temporary file remains in the files store but the database entry has been removed.

• Revert all DB modifications if any file store operation fails
• Ensure file store deletions are the final operation to occur in any request and exclude them from the reversion logic ^^
• Explore making file store changes transactional and also reversible (don't believe this is possible without storing everything in memory)

[b-zurg]

I recently came across an issue like this. This is an important improvement to the platform I think because if something does go wrong in a production release then it can break releasing from then on - unless you manually go into the database - as then, at least with the bug I'm facing, the release file generation is completely broken.