Initial Commint

Summary: Created "Applications" application which lists all the installed applications in phabricator.

Test Plan: Navigated to localphabricatorinstall.com/applications and check whether it actually shows the list of all installed applications.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2352

Differential Revision: https://secure.phabricator.com/D4548