Reorganize phui-object-item CSS, add drag ui

Summary: Reorgaizes the CSS here a bit, by object list style, adds in a new drag ui class, which will be used in menu ordering.

Test Plan:
Workboards, Home Apps.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D17057