The S3 implementation is far from finished, this commit focusses on the bases.
- Upgrade AWS SDK to latest version.
- Rewrite S3 Template downloader.
- Rewrite S3Utils utility class.
- Improve addImageStoreS3 API command.
- Split various classes for convenience.
- Various minor improvements and code optimalisations.
A side effect of the new AWS SDK is that it, by default, uses the V4 signature. Therefore I added an option to specify the Signer, so it stays compatible with previous versions.
