Fix broken pagination links

When you select another page or another content-type on the search page, Kete was just jumping to the first page of topics.

This was caused by the routes including `controller_name_for_zoom_class` in the url rather than the url-query:

    post 'for/(:controller_name_for_zoom_class)'            => 'search#for', as: :for

Changing them to this style worked:

    post 'for/'            => 'search#for', as: :for

and produced the `/for?controller_name_for_zoom_class=StillImage` style urls that work with will_paginate.

Let me know if there's a reason I'm not aware of why the second style is a bad idea.