When pagers aren't connected to an ObjectItemListView, put them in a little box

Summary: Pagers in Maniphest (and, to some degree, apps like Pholio) get lost a bit. Put them in a little box.

Test Plan: Looked at Maniphest and Pholio, pager was more obvious and less un-designed-looking.

Reviewers: chad, btrahan

Reviewed By: chad

CC: aran

Differential Revision: https://secure.phabricator.com/D6987