Add "final" to all Phabricator "Controller" classes

Summary:
These are all unambiguously unextensible. Issues I hit:

  - Maniphest Change/Diff controllers, just consolidated them.
  - Some search controllers incorrectly extend from "Search" but should extend from "SearchBase". This has no runtime effects.
  - D1836 introduced a closure, which we don't handle correctly (somewhat on purpose; we target PHP 5.2). See T962.

Test Plan: Ran "testEverythingImplemented" unit test to identify classes extending from `final` classes. Resolved issues.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran, epriestley

Maniphest Tasks: T795

Differential Revision: https://secure.phabricator.com/D1843

src/applications/differential/controller/changesetview/DifferentialChangesetViewController.php

@@ -16,7 +16,7 @@
  * limitations under the License.
  */
 
-class DifferentialChangesetViewController extends DifferentialController {
+final class DifferentialChangesetViewController extends DifferentialController {
 
 
   public function shouldRequireLogin() {