Allow YUI way of adding Handlebars helpers

[saich]

As per http://yuilibrary.com/yui/docs/handlebars/#defining-custom-helpers, the Handlebars helpers are defined using Y.Handlebars.registerHelper.

However, any helper registered using the above way are not available while generating views from hb templates on server.

Use case: Adding set of global handlebar helpers that works on both client and server. (helpers like pluralize, lowercase, uppercase, truncate etc. which are independent of mojit). More like, I want the Handlebars engine to be enhanced where I've access to a bigger set of helpers with almost no extra effort.

I understand ac.helpers.set and ac.helpers.expose are available, but I find a couple of concerns using this approach:

1. Needs access to ac which is available in each function of controller, and hence every function needs to attach these helpers.
2. Incompatibility with existing YUI code, which declared helpers this way.