Fixes https://github.com/thoughtbot/administrate/issues/1709
Using the param :page for top-level pagination (ie: index pages as opposed to has_many lists in show pages) conflicts with paginating resources whose type happens to be "Page".
I'd rather have written a unit spec for this, instead of a whole new dashboard for the example app. However the pagination code is all over the place making this quite tricky. Ideally, we should move all the pagination code into a single module that can be tested in isolation. This in turn is not easy, as Kaminari doesn't make it easy. I'm leaving that for another day.
I have created a new feature spec called pagination_spec.rb. Into this I have moved other pre-existing pagination examples, to help organise things, and also to take advantage of the helper method expect_to_appear_in_order in the new example.