Add ability to configure api_result_limit

In clouds with many containers or objects, listing them via Horizon
can cause a signficant increase of system load.

This patch enables configuration of the API_RESULT_LIMIT setting within
Horizon. This limits the maximum number of objects to display on a
single page before providing a paging element to paginate results.

Change-Id: Ifaf39d6c9bf549428afd7653243c82cd719956f6
Closes-Bug: 1775002