Update PeopleMenu to only show integration with applications if they are installed

Summary: do so via event engine. note different order now...

Test Plan: toggled "show beta applications" to off and noted that Conpherence disappeared. Otherwise noted that links showed.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2424

Differential Revision: https://secure.phabricator.com/D4708