Use /assets for client assets

- Route `/assets` -> `build/public`, falling back on `public`
- Moved destinations for `nodebb.min.js`, `acp.min.js`, `admin.css`, `stylesheet.css`, `templates`, and `sounds` to `build/public`
- r.js modules previously routed through express are now symlinked into `public/build/src/modules`
- minfiles no longer served from a memory cache
- use config `views_dir` setting everywhere template directory is used
- fix cache buster `v=v=`

public/src/widgets.js

@@ -29,7 +29,7 @@
 			}
 		});
 
-		$.get(config.relative_path + '/api/widgets/render' + (config['cache-buster'] ? '?v=' + config['cache-buster'] : ''), {
+		$.get(config.relative_path + '/api/widgets/render' + '?' + config['cache-buster'], {
 			locations: widgetLocations,
 			template: template + '.tpl',
 			url: url,