[CDS API] Accept-Encoding: gzip

[Will Lunniss]

Add support for responding to browse/search requests using gzip encoding.

While a lot of responses are quite small, some can be big (e.g Video->Movies, Audio->Albums, Image->Albums and potentially any folder views). Due to the repetitive nature of the resonses, they compress very well. E.g. my 600 Audio->Album response is normally 105KB, but it compresses down to 12KB using gzip encoding, movies go from 150KB to 30KB etc...