Remove manual `env === 'production'` checks.

We already have a `enabled` flag for each, why not use it?

Also, folks may need to minify other environemnts.
Merge pull request #1929 from rwjblue/remove-manual-production-checks

Remove manual `env === 'production'` checks.
Indicate tests as a directory in package.json

- the blueprint for app/files/package.con indicated test not tests
Merge pull request #1934 from pixelhandler/package-blueprint-package-json

Indicate tests as a directory in package.json
Moved modulePrefix to config/environment.js
Merge pull request #1933 from jayphelps/module-prefix

Moved modulePrefix to config/environment.js
Allow array of paths to the preprocessCss phase

- Ensure backwards compat for app.scss -> <app name>.css