Upgrade to latest Meteor API

[boustanihani]

I think meteor-addons.js needs a small updgrade, according to:
https://github.com/meteor/meteor/blob/devel/History.md#backwards-compatible-blaze-api-changes

UI, UI.insert and UI.renderWithData has been deprecated. We should now use Blaze.render() and Blaze.renderWithData() instead...

Check:

• http://docs.meteor.com/#/full/blaze_render
• http://docs.meteor.com/#/full/blaze_renderwithdata

[cwohlman]

Correct, I've been seeing errors about that in my console for a while. It's on the back burner for now, but I'd certainly have time to review and merge a pull request.