Paginate all, individual and company contributors

:fork_and_knife: The contributors lists are getting a bit long and costly when rendering the page so let's paginate them.
I think it'd be worth paginating in SQL. Locally, with a few hundred contributors, the query for the first page is about 10x faster than the array equivalent. SQL unfortunately becomes about as slow as Kaminari's `paginate_array` as the page number increases (somewhere between page 10 and page 15 seems to be the intersection).