Allow the use of bower for external dependencies.

This is really just meant as a way to help the conversation in #24. The
basic gist of what I have done is to setup bower to use vendor/ as its
work directory and updated the various supporting files to use the new
subfolder structure (bower stores it's dependencies in subfolders).

This makes it significantly easier to keep a project made with this repo
as a base up to date since all that would be needed would be to update
the bower.json to point to the current version of Ember, jQuery, and
Handlebars, and run `bower install`.

I wasn't sure if we wanted to add an explicit bower dependency so I
added the required files explicitly in 4c5da28...

I believe at this point if a 'consumer' wants to use bower all they
would need to do is 'bower install', but if not then the repo still
works properly.