Add the buildExpiration config and add it to the renderer's config
object. Use grunt to write the build expiration to
config/local-production.json which will override the default value (no
expiration) in production. Finally, run this grunt task as part of the
build process.
// FREEBIE
Add environment-specific configs under `./config` and integrate with the
build system. Also changes package.json `files` from blacklist to
whitelist.
// FREEBIE
