Add "final" to more classes

Summary: No big surprises here, delted the unused "DarkConsole" class.

Test Plan: Ran 'testEverythingImplemented' to verify I wasn't finalizing anything we extend.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran, epriestley

Maniphest Tasks: T795

Differential Revision: https://secure.phabricator.com/D1876

src/applications/differential/storage/diff/DifferentialDiff.php

@@ -16,7 +16,7 @@
  * limitations under the License.
  */
 
-class DifferentialDiff extends DifferentialDAO {
+final class DifferentialDiff extends DifferentialDAO {
 
   protected $revisionID;
   protected $authorPHID;