Panels list: fix missing welcome page

Summary:
The method getNewUserBody() was never designed for a list controller.
The method was just orphan. Now, instead, it's non-orphan, and it works
as expected.

This bug was highlighted by Andre Klapper, since their linter was screaming
about inconsistences in the current nonsense usage of getNewUserBody():

D25649

The code was just moved from the list controller, to the search engine.

- PhabricatorDashboardPanelListController (from)
- PhabricatorDashboardPanelSearchEngine (to)

Bonus point:

Adjusted the icon and the title to talk about "Panels" and not "Dashboards".

Added also some inline documentation with an hint about `?nux=1`.
So now we can easily remember how to test this kind of things.

Closes T15844

Test Plan:
In both these pages, you finally see a welcome message, not just in Maniphest:

- http://phorge.localhost/dashboard/panel/?nux=1
- http://phorge.localhost/maniphest/?nux=1

In both these pages, if you have no elements, you finally see a welcome message,
and not just in Maniphest:

- http://phorge.localhost/dashboard/panel/
- http://phorge.localhost/maniphest/

Check that the welcome message helps you in creating a new Panel, and that
talks about Panels, and that have the lovely icon of a Panel.

Reviewers: aklapper, O1 Blessed Committers

Reviewed By: aklapper, O1 Blessed Committers

Subscribers: tobiaswiese, Matthew, Cigaryno

Maniphest Tasks: T15844

Differential Revision: https://we.phorge.it/D25674

src/applications/dashboard/controller/panel/PhabricatorDashboardPanelListController.php

@@ -48,23 +48,4 @@ final class PhabricatorDashboardPanelListController
     return $crumbs;
   }
 
-  protected function getNewUserBody() {
-    $create_button = id(new PHUIButtonView())
-      ->setTag('a')
-      ->setText(pht('Create a Panel'))
-      ->setHref('/dashboard/panel/edit/')
-      ->setColor(PHUIButtonView::GREEN);
-
-    $icon = $this->getApplication()->getIcon();
-    $app_name =  $this->getApplication()->getName();
-    $view = id(new PHUIBigInfoView())
-      ->setIcon($icon)
-      ->setTitle(pht('Welcome to %s', $app_name))
-      ->setDescription(
-        pht('Build individual panels to display on your homepage dashboard.'))
-      ->addAction($create_button);
-
-      return $view;
-  }
-
 }

src/applications/dashboard/query/PhabricatorDashboardPanelSearchEngine.php

@@ -147,4 +147,22 @@ final class PhabricatorDashboardPanelSearchEngine
     return $result;
   }
 
+  protected function getNewUserBody() {
+    $create_button = id(new PHUIButtonView())
+      ->setTag('a')
+      ->setText(pht('Create a Panel'))
+      ->setHref('/dashboard/panel/edit/')
+      ->setColor(PHUIButtonView::GREEN);
+
+    $app_name = pht('Panels');
+    $view = id(new PHUIBigInfoView())
+      ->setIcon('fa-line-chart')
+      ->setTitle(pht('Welcome to %s', $app_name))
+      ->setDescription(
+        pht('Build individual panels to display on your homepage dashboard.'))
+      ->addAction($create_button);
+
+      return $view;
+  }
+
 }

src/applications/search/engine/PhabricatorApplicationSearchEngine.php

@@ -1454,6 +1454,12 @@ abstract class PhabricatorApplicationSearchEngine extends Phobject {
     return $attachments;
   }
 
+  /**
+   * Render a content body (if available) to onboard new users.
+   * This body is usually visible when you have no elements in a list,
+   * or when you force the rendering on a list with the `?nux=1` URL.
+   * @return wild|PhutilSafeHTML|null
+   */
   final public function renderNewUserView() {
     $body = $this->getNewUserBody();
 
@@ -1464,6 +1470,12 @@ abstract class PhabricatorApplicationSearchEngine extends Phobject {
     return $body;
   }
 
+  /**
+   * Get a content body to onboard new users.
+   * Traditionally this content is shown from an empty list, to explain
+   * what a certain entity does, and how to create a new one.
+   * @return wild|PhutilSafeHTML|null
+   */
   protected function getNewUserHeader() {
     return null;
   }