(TK-75) Make Gzip encoding configurable for the Jetty webserver

This commit adds an option to the webserver configuration,
`gzip-enable`, which can be used to control whether or not the webserver
would attempt to compress the response body using Gzip encoding.
Merge pull request #77 from camlow325/feature/master/TK-75-make-gzip-encoding-configurable

(TK-75) Make Gzip encoding configurable for the Jetty webserver