Turn the "closed" property on cluster repositories into a nice boolean

Summary:
Ref T10883. Ref T13120. There's an existing "closed" property on repository services that stops new repositories from being allocated there.

Turn it into a nice boolean.

Test Plan: Toggled the value on/off using a nice `<select />` with helpful labels instead of a text area.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13120, T10883

Differential Revision: https://secure.phabricator.com/D19355

src/applications/almanac/servicetype/AlmanacClusterRepositoryServiceType.php

@@ -20,7 +20,11 @@ final class AlmanacClusterRepositoryServiceType
 
   public function getFieldSpecifications() {
     return array(
-      'closed' => id(new PhabricatorTextEditField()),
+      'closed' => id(new PhabricatorBoolEditField())
+        ->setOptions(
+          pht('Allow New Repositories'),
+          pht('Prevent New Repositories'))
+        ->setValue(false),
     );
   }