S3 file store and fetch

[bacosmin]

on each save if the keys are set the app will store also on s3
This is useful for Heroku since it is has readonly file system .

[mose]

Neat addition :)

It may require some extra work, for a more modular approach of the storage method and have an appropriate test coverage.

I also wonder how the I18n backend facility evolved recently, because this kind of modulratity could have been delegated to that class, I think. Gotta check that as.

Anyways, I will check and test this change soon and merge if it doesn't break things. We can add some refactoring later down the road for modularity.