Split out vendored handlebars.js in favor of using
a version of handlebars.js wrapped in the
handlebars-source gem.

Also created ember-source.gemspec
as an analogue to to handlebars-source that will wrap
all /dist ember distros.
Merge pull request #2137 from machty/handlebars-source

Split out handlebars from ember-template-compiler; now we use handlebars...