Use jquery-ui-rails for jQuery UI

Spree uses jquery-rails ~>3.0.0 as of commit
ea5610378c11baafa85eea87543d563d982ceaab.
This version doesn't include jquery-ui, so jquery-ui-rails is now
included.

Fixes #48
Fixes #50

Change-Id: Id0503b61f81330d4e20f0b75ed2eee4d9cfc0d28