Return $this from setters

Summary:
Most setters returns `$this` but some don't.
I guess it's not by purpose.

Test Plan:
  arc lint

Reviewers: epriestley

Reviewed By: epriestley

CC: aran

Differential Revision: https://secure.phabricator.com/D2085

src/applications/project/editor/project/PhabricatorProjectEditor.php

@@ -157,6 +157,7 @@ final class PhabricatorProjectEditor {
       default:
         throw new Exception("Unknown transaction type '{$type}'!");
     }
+    return $this;
   }
 
   private function applyTransactionEffect(