Convert the "Repository Management" UI to a full-width, Phortune-style UI

Summary:
Ref T13216. I want to add some new management options to repositories (e.g., filesize limit, clone timeouts). Before adding new stuff here, update the UI to a full-width, Phortune-style UI.

This partially reverts D18523. About a year ago, several UIs got converted to fixed-width (repository management, config, settings, instance management in SAAS). I didn't think these were good changes and have never really gotten used to them. The rationale wasn't clear to me and these changes just felt like "be more like GitHub". I think usability is significantly worse, e.g. actions are now hidden inside button menus instead of immediately visible.

Phortune also got converted less dramatically to a full-width-with-menu UI, which I like much better. Adjust repository management to use that UI style instead of the fixed-width style.

Test Plan:
{F6020884}

Viewed every panel, including the Subversion panel.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13216

Differential Revision: https://secure.phabricator.com/D19826

src/applications/diffusion/controller/DiffusionRepositoryManagePanelsController.php

@@ -68,13 +68,17 @@ final class DiffusionRepositoryManagePanelsController
 
     $view = id(new PHUITwoColumnView())
       ->setHeader($header)
-      ->setNavigation($nav)
-      ->setFixed(true)
       ->setMainColumn($content);
 
+    $curtain = $panel->buildManagementPanelCurtain();
+    if ($curtain) {
+      $view->setCurtain($curtain);
+    }
+
     return $this->newPage()
       ->setTitle($title)
       ->setCrumbs($crumbs)
+      ->setNavigation($nav)
       ->appendChild($view);
   }