Add a new pagination setting 'TEMPLATE_PAGINATION' which allows the user to set the number of pages used on a per-template basis.

This change adds a new setting 'TEMPLATE_PAGINATION', which may be used when
you want a specific page to have a different pagination value than the default.

For example, you want an index page with 10 articles per page, but category
pages should have 3 articles per page.

(This change includes update to docs/settings.rst which explains how to use the setting)