Source map temp fixes

Some housekeeping to release beta 14.1. We need beta14.1 as due to the `<%= versionStamp %>` (which was fixed recently by @tricknotes in https://github.com/emberjs/data/pull/2631) and also to note the dropped compatibility for Ember <= 1.7.1(http://emberjs.com/blog/2014/11/24/ember-data-1-0-beta-12-released.html)

Adds sourcemap support in ember-cli due to a comment on the blog http://emberjs.com/blog/2014/12/25/ember-data-1-0-beta-14-released.html.
I believe that you can use `-1.8` actually (from https://getcomposer.org/doc/faqs/why-are-unbound-version-constraints-a-bad-idea.md).