Production build should:

• no console.log or debug output
• js uglified and css minified (with no source mapping?)
• image files optimized

Debug (devel) build should:

• support console.log or debug output
• js and css not minified or uglified
• image files not optimized

--debug option can be passed from gulp (gulp --debug), or set it in ./config.json:

{
  "debug": true
}