Compress static resources

[ekuiter]

Right now, static resources (CSS, JavaScript) are served as-is in Jetty and Tomcat. Instead, they should be transferred with GZIP compression enabled.

(Actually, serving static resources from a "dynamic" servlet container is not that smart. It would be better to use a CDN/S3 bucket for this purpose because these are optimized on static content. But as the editor should work stand-alone and not depend on any online resources (and versioning), we will most likely keep this approach.)