Store gzip representations of common files on deploy

[jbergstroem]

Since we're using gzip_static on in the server we could shave off an considerable amount of cpu power by storing a gzip representation of each file we deploy (for instance index.html would be accompanied by index.html.gz). Additionally, since we default to -6 in nginx, we'd likely make each file a bit smaller by using -9 on deploy.

[fhemberger]

We could add a npm task, which is only run on the build machine:
find -E build -type f -regex ".*(html|css|js|xml|json)$" -exec gzip -9 -k {} \;

Takes 0.75s on my MacBook Pro for the current website.