chore(webui): better build command

- clean before build (mode force)
- update documentation
- update `Makefile`
- ordering build

webui/gulp/build.js

@@ -92,7 +92,7 @@ gulp.task('other', function () {
 });
 
 gulp.task('clean', function () {
-  return $.del([path.join(conf.paths.dist, '/'), path.join(conf.paths.tmp, '/')]);
+  return $.del([path.join(conf.paths.dist, '/**'), '!' + conf.paths.dist, path.join(conf.paths.tmp, '/')], {force: true});
 });
 
 gulp.task('build', ['html', 'fonts', 'other']);