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.
what has precedence?
stream or callback?
I mean will gulp wait for stream even if cb has been called?