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
The default XHR error handler produce an alert which is appropriate to the response status code. It can be overridden per-request (by specifying the `errorHandler` option) so that the alert can be suppressed or displayed in a different position (e.g. inside a modal).
ref #118
Adds app.trans calls for strings used by the admin UI.
- Strings for AddExtensionModal.js not included.
- Corresponding YAML will be sent later w/ more extracted strings.
