Adds navbar to `layouts.default` using include/partial

- Adds `views/layouts/partials` directory
    - Adds `nav.blade.php` w/ boilerplate/temp content
Adds `app/assets/sass` directory
Adds npm dependencies and Gulpfile.js

- package.json dependencies
    - `"gulp": "^3.8.6"`
    - `"gulp-autoprefixer": "0.0.8"`
    - `"gulp-sass": "^0.7.2"`
- Gulpfile dirs
    - dirs.assets = 'app/assets/
    - dirs.dest   = 'public/dist/ <- add to .gitignore
- Gulpfile tasks
    - css
    - watch
    - default -> ['watch']
Adds <link> to compiled .css and minimal content in .scss file