Add wrapping for AMD modules

[jas]

This allows use of https://github.com/stefanpenner/ember-jj-abrams-resolver which can load templates from AMD modules instead of Ember.TEMPLATES

When modules.wrapper is set to "amd", Brunch handles adding the module name to the define wrapper function.

Example output after being processed through Brunch. modules.nameCleaner option can be used to remove app/ module prefix.

define("app/templates/index", [], function() {
  return Ember.Handlebars.template(function anonymous(Handlebars,depth0,helpers,partials,data) {
    this.compilerInfo = [4,'>= 1.0.0'];
    helpers = this.merge(helpers, Ember.Handlebars.helpers); data = data || {};
    data.buffer.push("<p>Hello, world!</p>\n");
  });
});

This could be cleaner if we replace modulePrefix with the wrapper function, but I left it for backwards compatibility in case anyone is overriding it.