Installation & Uninstallion of Applications

Summary: Created Applications application which allows uninstallation & installation of application.

Test Plan: In "Applications" application, clicked on uninstalled the application by cliking Uninstall and chekcing whether they are really uninstalled(Disabling URI & in appearance in the side pane). Then Clicked on the install button of the uninstalled application to check whether they are installed.

Reviewers: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D4715