Start of a config web interface.

Summary:
This is somewhat clowny, particularly in how it handles JSON encode/decode, but
I've commented why I did things the way I did. The goal is to store minified JSON
but show pretty-printed JSON where possible, to the user editing it.

Test Plan:
* Went to /config/ and saw a list of keys from the `default` config.
* Clicked on one of them, submitted the default value successfully.
* Changed the value to invalid JSON and got a decent error.
* Changed the value to valid JSON and checked the DB to confirm it saved.
* Confirmed the DB values were minified.
* Confirmed the user-facing values were pretty-printed where they could be.
* Confirmed that PHIDs were getting assigned properly and that isDeleted
  properly defaulted to false/0.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2246

Differential Revision: https://secure.phabricator.com/D4290

src/applications/config/controller/PhabricatorConfigController.php

@@ -0,0 +1,27 @@
+<?php
+
+abstract class PhabricatorConfigController extends PhabricatorController {
+
+  public function shouldRequireAdmin() {
+    return true;
+  }
+
+  public function buildSideNavView($filter = null, $for_app = false) {
+    $user = $this->getRequest()->getUser();
+
+    $nav = new AphrontSideNavFilterView();
+    $nav->setBaseURI(new PhutilURI($this->getApplicationURI('filter/')));
+
+    return $nav;
+  }
+
+  public function buildApplicationMenu() {
+    return $this->buildSideNavView(null, true)->getMenu();
+  }
+
+  public function buildApplicationCrumbs() {
+    $crumbs = parent::buildApplicationCrumbs();
+    return $crumbs;
+  }
+
+}