Adding a Paginator to fix Kaminari & WillPaginate conflicts.

Alternatively we could use the solution active_admin uses 
(make the user define a new per_page_method for Kaminari) 
but that either puts more work on the user's end, or has 
the potential side effect of breaking other gems. This 
way isn't perfect (our page select html in views are 
rendered differently for will_paginate and kaminari) but
it seems like a solid start that prevents any extra work
for users of upmin-admin.