Make pagination tunable through the settings panel

This patch set expands on the fine work done in https://review.openstack.org/26022

It makes the number of items displayed a per-user tunable through
the "Settings" panel and a session cookie, with the default/max
values being the values set in django.conf.settings

Fixes Bug: 1046915
Change-Id: I38ef4845d46bce62e44209865885aff8eb0bac83
Merge "Make pagination tunable through the settings panel"