Set S3 permissions during file write

I've added this since with GaufretteBundle you can't use AclAwareAmazonS3 and this would be a nice way to set file permissions on write.
Added acl into class options and acl getter/setter
Merge branch 'patch-1' of https://github.com/alex88/Gaufrette into alex88-patch-1
Add spec for acl handling in amazon adapter. Renaming of spec methods.