Make sure we can run `rake cucumber` without error.

Some files were missing, but most importantly, because
of an incompatibility between cucumber and rails 4,
I had to use the an unreleased version of cucumber
that fixes that error. See https://github.com/cucumber/cucumber-rails/pull/253
Define HomeController and index action.
Needed to move jquery-rails out of assets group.

Confused, not sure why, does not work otherwise.
Implement first cucumber step: we can now visit the home-page.
Merge pull request #1 from nathanvda/master

First pull request!