use libsass and update build system

common/gnome-shell/3.16/gulpfile.js

@@ -0,0 +1,18 @@
+var gulp        = require("gulp");
+var sass        = require("gulp-sass");
+var filter      = require('gulp-filter');
+
+gulp.task('sass', function () {
+    return gulp.src('sass/*.scss')
+        .pipe(sass({
+            outputStyle: 'nested',
+            precision: 5,
+            onError: function (err) {
+                notify().write(err);
+            }
+        }))
+        .pipe(gulp.dest('.'))
+});
+
+
+gulp.task('default', ['sass']);