HG-119: Gzip resources on build step

Moved the `build.js` task to `build-all.js`. The new build task depends on `build-all` and only compresses the static resources if the environment is production.

The reason for that is that we need all the resources prepared, before `gzip`-ing them. Doing this on the fly leaves only the gzipped files without the originals, which we still need in case the client does not support compressed resources.
The package is not touched for 6 months, so it may not be so soon :) Since that's a sign the code is stable :station: