INTEXT-60 Add support for AWS S3 Gateway in the AWS adapters

Apart from the AWS S3 Outbound and inbound adapters, a gateway was needed to let the application invoke an operation on the bucket. The supported operations are
 * List Objects in a bucket
 * Remove Object from a bucket
 * Put objects in a bucket
 * Get contents of a object in the bucket

The JIRA [INTEXT-60] is created for the same purpose

[INTEXT-60]:https://jira.springsource.org/browse/INTEXT-60