Allow disabling previous and next page checks

[StijnKing]

trafficstars

Problem

When we use this gem it causes two count queries before the actual query happens. But because of performance reasons we want to avoid having these count queries. So I would like to propose this PR (or something similar).

Reason

The previous_page? and next_page? methods in certain cases require a count query in order to determine if the next/previous pages exists. These count queries can be expensive so an option to disable these checks are added.

For backwards compatibility these checks are enabled by default.