Enable CMS paginated content to be configured at Liquid Template

Request to implement a way to change per_page Liquid Template variable at 3scale CMS. This could allow customers to customize the output size of the generated paginated table.

For example, at Applications/Index we can use at the top:

    {% assign pagination.per_page = 500 %}
    Pagination:<br />
    Current page: {{ pagination.current_page }}<br />
    Page_size: {{ pagination.page_size }}<br />
    Per_page: {{ pagination.per_page }}<br /><br />

This will result on:

Pagination:
Current page: 1
Page_size: 30
Per_page:

The per_page is a protected variable (as we can see here: https://github.com/3scale/porta/blob/5fac953d4ce2b8c1508d58cb4d5d76fed27b2812/app/controllers/admin/api/filters/pagination.rb#L60). It can't be changed even using per_page query variable.

Also, the page_size variable are controlled by per_page, as seen here: https://github.com/3scale/porta/blob/master/lib/developer_portal/lib/liquid/drops/pagination.rb#L68-L70.

Note: I've also tested to modify page_size variable, without success.