Smooth out milestone creation workflow

Summary:
Ref T10010.

  - Default name to "Milestone X".
  - Remove policy controls, which have no effect.
  - Don't generate slugs for milestones since this is a big pain where they all generate as `#milestone_1` by default (you can add one if you want). I plan to add some kind of syntax like `#parent/32` to mean "Milestone 32 in Parent" later.
  - Don't require projects to have unique names (again, 900 copies of "Milestone X"). I think we can trust users to sort this out for themselves since modern Phabricator has "Can Create Projects" permission, etc.

Test Plan: Created some milestones, had a less awful experience.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10010

Differential Revision: https://secure.phabricator.com/D14909

src/applications/project/controller/PhabricatorProjectProfileController.php

@@ -186,7 +186,9 @@ final class PhabricatorProjectProfileController
         ->setName('#'.$slug->getSlug());
     }
 
-    $view->addProperty(pht('Hashtags'), phutil_implode_html(' ', $hashtags));
+    if ($hashtags) {
+      $view->addProperty(pht('Hashtags'), phutil_implode_html(' ', $hashtags));
+    }
 
     $view->addProperty(
       pht('Members'),