Provide a way to compile less or sass application

Hello,

Perhaps I have miss something in the documention, but since component style are kinda hard to override from external , it would be great if you can by default process less and sass application.

Exemple to process less application in "src/less/**" : **gulpfile.js**

```
var p = require('gulp-load-plugins')();
var less = require('gulp-less');
var cleanCSS = require('clean-css');

/**
* Process less application
*/
gulp.task('process-css', function () {
var src = ['src/less/**/*.less'];

return gulp.src(src)
.pipe(less({}))
.pipe(p.concat('styles.css'))
.pipe(p.sizereport({
gzip: true,
total: false,
minifier: function (contents, filepath) {
return new cleanCSS().minify(contents).styles;
}
}))
.pipe(p.cleanCss())
.pipe(gulp.dest('dist/styles'));
});
```

**package.json** file :

```
"gulp-less": "3.1.0",
"gulp-clean-css": "^2.0.6",
"gulp-load-plugins": "^0.10.0",
"gulp-sizereport": "^1.1.3",
"gulp-concat": "^2.5.2"
```

Thanks