Build LauncherButton for PHUIObjectItemView

Summary: There are a handful of places I've been wanting to use a button here. Adds that ability and uses in app launcher.

Test Plan:
Test Applicatons->Launcher at desktop, mobile, tablet breakpoints

{F780453}

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D14059