Automatically support basic HTML tags in translations

This allows front-end translations to use basic (attributeless) HTML tags freely, without the need for the translator call to supply a matching vdom element. Translations can thus make use of styling (<em>, <code>, etc.) as they see fit. The translator call can still optionally supply a vdom element to substitute in more complex tags where necessary (e.g. hyperlinks).

/cc @dcsjapan

js/lib/Translator.js

@@ -74,7 +74,7 @@ export default class Translator {
           if (match[2]) {
             open.shift();
           } else {
-            let tag = input[match[3]] || [];
+            let tag = input[match[3]] || {tag: match[3], children: []};
             open[0].push(tag);
             open.unshift(tag.children || tag);
           }