allow user to set the kaminari page method

So I'm trying to put wice_grid into an app that uses will_paginate.  Rather than changing everything over to kaminari (which might not be a bad idea), I'm trying to use both simultaneously.  Kaminari supports `config.page_method_name = <method_symbol>` that allows you to use a method other than `page` to do your paginatation.  I've set this up, but wice_grid expects the kaminari page method to be called `page`.  I suppose we could get the method from kamanari itself but I thought it might be simplest just to add an option to set the name of the `page` method, both in the defaults so it can be set at config time, as well as when setting up the grid (just because, really).  I can add tests if you like but I was not sure how to handle that since tests are in a different repo.  Thanks for your consideration and so far your gem is looking great.  I look forward to using it more.