Deprecate 'maniphest.enabled' and 'phriction.enabled'

Summary:
Also join concepts of installed and enabled applications.
Also respect uninstalled Maniphest where disabled Maniphest was checked.

Test Plan:
Visited T1, D1.
Uninstalled Maniphest then visited T1, D1.
Disabled Maniphest then visited T1.
Visited /config/edit/maniphest.enabled/.

Reviewers: epriestley, Afaque_Hussain, edward

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D5602

src/applications/directory/controller/PhabricatorDirectoryMainController.php

@@ -30,7 +30,8 @@ final class PhabricatorDirectoryMainController
   private function buildMainResponse($nav, array $projects) {
     assert_instances_of($projects, 'PhabricatorProject');
 
-    if (PhabricatorEnv::getEnvConfig('maniphest.enabled')) {
+    $maniphest = 'PhabricatorApplicationManiphest';
+    if (PhabricatorApplication::isClassInstalled($maniphest)) {
       $unbreak_panel = $this->buildUnbreakNowPanel();
       $triage_panel = $this->buildNeedsTriagePanel($projects);
       $tasks_panel = $this->buildTasksPanel();