Decouple Administrate from Kaminari

[pablobm]

We have several reports about problems with Kaminari, the gem we use for pagination. These are marked as pagination how we handle lots of data in small chunks and include:

• Kaminari pagination conflict with installed gem #1838
• Pagination can get slower over time #2220
• Model named "Template" won't show index in admin #2281

Last time I checked, Kaminari worked in a very "global" manner, making it difficult to enable/disable at will. It seemed very "all or nothing". Users have other pagination solutions in their apps, and loading Kaminari as well can cause issues. Also Kaminari overloads ActiveRecord, leading to more issues.

Ideally, we should isolate Kaminari and offer a way to opt out of it and use other gems, in a way similar to how we offer Pundit support as a separate add-on.