Implemented support for turbolinks, when it's present.

To enable it, just place it in the Gemfile of your application:

```ruby
gem 'jquery-turbolinks'
gem 'turbolinks'
```

Bugs that need fixing include: some tests fail

This does _not_ place a dependency on turbolinks, it has to be in the Gemfile!
Like this?

```erb
<%= refinery_turbolinks_include_tags %>
```

```ruby
def refinery_turbolinks_include_tags
  tags = []
  tags << javascript_include_tag('jquery.turbolinks') if defined?(JqueryTurbolinks)
  tags << javascript_include_tag('turbolinks') if defined?(Turbolinks)
  tags.join('\n')
end
```

?