Switched to database-based tracking for page editor

- Works better to avoid bad assumptions when showing the editor based
  upon content type.
- Also updated some previous tests to cleaner format.

app/Entities/Models/Page.php

@@ -22,6 +22,7 @@ use Illuminate\Database\Eloquent\Relations\HasOne;
  * @property bool         $template
  * @property bool         $draft
  * @property int          $revision_count
+ * @property string       $editor
  * @property Chapter      $chapter
  * @property Collection   $attachments
  * @property Collection   $revisions