Move pagination plugin to core

[ricardograca]

• Related Issues: Promote some useful plugins to core #1806

Introduction

Move the pagination plugin to core Bookshelf.

Motivation

This is a very useful plugin and its functionality should be part of core since it's almost always used and, in fact, even the documentation has .fetchPage() as a Model method, even though it's currently only available if you call .plugin('pagination').

Proposed solution

Base functionality is moved to the lib/helpers.js file so it can be shared between model and collection methods. New fetchPage methods are added to Model and Collection. No functionality was removed.