Add compression for sync streams

[magnetised]

The sync messages benefit greatly from compression - make sure both embedded mode and http mode add or maintain compression.

[evanob]

After a little bit of investigation, this seems a caused by the combination of two things:

1. strong etag set in the headers tells web server not to compress
2. streaming response when chunked: true is set on Shapes.Api.Response, and it seems that streaming and compression are incompatible

With compression, we sometimes see more than 10x reduction in payload, so we would like to take advantage of that. I think we could compress on a CDN, but only if the response is not streaming, so it would be great if that could be configurable.