R1:0700bb2aca67

Add a selected color state to PHUIPagerView

Summary: This probably got nuked at some point, but the class is there so let's use it.

Test Plan: Browse a directory with 800 files. See pager change color.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D18089