JetS3 migrated to AWS SDK + Unit tests

Here is a first version based on AWS SDK!

I've added bucket creation capabilities with save() to S3Directory and getURL(expirationDate) to S3CloudFile to get pre-signed URL.

By default, ACL is set to private, but you can pass a cannedACL when saving a file.

```groovy
s3[bucketName]['test.txt'].text("Setting the text value").save(CannedAccessControlList.PublicRead)
```