Basic Gulp scaffold

Setup build environments with CLI arguments.
  - default to 'development'
  - pass `--env [p|prod|production]` for 'production' mode

Styles
  - compile SCSS
  - concat into single file
  - autoprefixer
  - minify (CSSO, in 'production' only)

Scripts
  - JSHint
  - concat into single file
  - uglify (in 'production' only)

Compile SCSS into a single CSS file

Lint and contat JS into a single file