Adds CSS source maps to debugging builds

[ajmueller]

This change to the build process will add CSS source maps when debugging is enabled. Due to restrictions of the gulp-sourcemaps package, there is one minor concern: both autoprefixer and combine media queries had to be moved to only execute on non-debugging builds (e.g. production). This is due to restrictions on which plugins support Gulp source maps. You'll see autoprefixer is on that list, though I was not able to get it to work properly. Let me know if you get this to work properly.

This restriction would mean that builds, particularly non-debugging builds, will need to be tested thoroughly before a release and prefix-related issues could arise with debugging builds. Despite this, I believe the pros of having access to CSS source maps far outweigh these cons.

If you'd like to test this branch, you'll probably want to take a look at how to utilize the source maps in your browser of choice:

• Chrome - official Google doc or Sass Bites video podcast, a quick run-through by Micah Godbolt, the organizer of PDX Sass
• Firefox
• Internet Explorer (if you're so inclined; I haven't tested this)

[ajmueller]

For anyone who wants to embark on getting both Sass compilation and autoprefixer working with source maps, here are the things I've tried to no avail:

• updating autoprefixer and its options syntax. I've pushed this to the feature branch to keep it up-to-date, but have kept autoprefixer as only running in non-debugging builds.
• changing order of the build steps, though the steps should be fairly set in stone (as determined by the gulp-sass and gulp-autoprefixer documentation:
  • initialize source map
  • compile Sass
  • prefix compiled CSS
  • write source map

Overall I don't think we are at much of a disadvantage by adding prefixes and combining media queries on only non-debugging builds, but as noted above it will make testing those builds even more important.