Modernize most somewhat-weird Diffusion controllers

Summary: Ref T4245. This gets everything else except serving HTTP requests (complicated) and lint (quite weird).

Test Plan:
  - Viewed a diff.
  - Viewed externals.
  - Viewed history table to see last modified.
  - Did path completion and validation in Owners.
  - Did tree path search in Diffusion.
  - Viewed a repository.
  - Created a new repository.
  - Looked up symbols.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T4245

Differential Revision: https://secure.phabricator.com/D14947

src/applications/diffusion/controller/DiffusionLastModifiedController.php

@@ -6,9 +6,14 @@ final class DiffusionLastModifiedController extends DiffusionController {
     return true;
   }
 
-  protected function processDiffusionRequest(AphrontRequest $request) {
+  public function handleRequest(AphrontRequest $request) {
+    $response = $this->loadDiffusionContext();
+    if ($response) {
+      return $response;
+    }
+
+    $viewer = $this->getViewer();
     $drequest = $this->getDiffusionRequest();
-    $viewer = $request->getUser();
 
     $paths = $request->getStr('paths');
     try {