Support Spaces in Diffusion

Summary:
Ref T8493. Diffusion is probably the strongest upstream use case we have for Spaces right now, so I want to get us on it to kick the tires a bit.

Small amount of hackiness around the multi-page form thing but it shouldn't create any problems.

Test Plan:
  - Created a new repo.
  - Edited a repo.
  - Tried invalid edits, saw value preserved.
  - Viewed edit full detail screen, saw space info.
  - Viewed repo detail view, saw space.
  - Viewed repo list view, saw space.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T8493

Differential Revision: https://secure.phabricator.com/D13414

src/applications/repository/query/PhabricatorRepositorySearchEngine.php

@@ -153,6 +153,7 @@ final class PhabricatorRepositorySearchEngine
 
       $item = id(new PHUIObjectItemView())
         ->setUser($viewer)
+        ->setObject($repository)
         ->setHeader($repository->getName())
         ->setObjectName('r'.$repository->getCallsign())
         ->setHref($this->getApplicationURI($repository->getCallsign().'/'));