JCLOUDS-400: Allow the HeaderParam annotation to be used in a Caller.

This allows jclouds to factor out common headers into the Caller so they don't
have to be repeated in the Callee.

The Produces/Consumes annotations (Content-Type/Accept headers) will also
propagate from the Caller to the Callee.
JCLOUDS-356 multipart uploads with InputStream payloads

This changeset introduces an alternative to PayloadSlicer,
IterablePayloadSlicer, with a method for returning a Payload iterator.

...swift.blobstore.strategy.internal.SequentialMultipartUploadStrategy
has been updated to to use a payload iterator.
[JCLOUDS-263] Usage of internalURL services' endpoints