Adds test for Kaminari page_url_for helper url scoping.

We added a scope option to the kaminari paginator helper. If that is present, then the url_for method is called on that routes proxy object. This commit adds a test for that hack.
Use an alchemy theme for Kaminari pagination links.

This ensures that the Kaminari options from the host app could not override the pagination look and feel of Alchemy.