Improved kaminari support

Problem: searchkick does not play nice together with kaminari.

Details: kaminari has `link_to_previous_page` and `link_to_next_page` helpers which depend on `first_page?` and `last_page?` methods (https://github.com/amatsuda/kaminari/blob/master/lib/kaminari/helpers/action_view_extension.rb#L42).

I added those methods to improve kaminari support.