Update changelog for 0.7.4 release
lein-release plugin: preparing 0.7.4 release
lein-release plugin: bumped version from 0.7.4 to 0.7.5-SNAPSHOT for next development cycle
(TK-57) 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.