Move views for into fake_app/rails_views
Divide specifications of decorators and models from rails_app
Add spec for Sinatra app

It runs with the fllowing command:

  `BUNDLER_GEMFILE=gemfiles/Gemfile-sinatra bundle exec rake spec:sinatra`

Sinatra doesn't support implicit object rendering (like `render @author`),
so features about this won't tested in the partial spec. This switching
is made with `rails?` method decrared in spec_helper.rb.
Add activesupport (>= 3.0.0) dependency

activesupport gem isn't installed with Sinatra by default.