Provide basic capabilities to make Differential column width flexible

Summary:
- Make wrap width settable in PHP.
  - Dynamically generate max-width based on configurable maximum width.
  - Constrain non-diff elements to standard width.
  - Provide a configuration setting.

Test Plan:
Set various things to 100 / 120, as far as I could tell everything seemed to
render sensibly? This should have no effect on 80-col changes.

Reviewed By: jdperlow
Reviewers: jdperlow, tuomaspelkonen, jungejason, aran
CC: aran, jdperlow
Differential Revision: 413

src/applications/differential/controller/diffview/DifferentialDiffViewController.php

@@ -117,15 +117,14 @@ class DifferentialDiffViewController extends DifferentialController {
       ->setRenderingReferences($refs);
 
     return $this->buildStandardPageResponse(
-      '<div class="differential-primary-pane">'.
-        implode(
-          "\n",
+      id(new DifferentialPrimaryPaneView())
+        ->setLineWidthFromChangesets($changesets)
+        ->appendChild(
           array(
             $top_panel->render(),
             $table_of_contents->render(),
             $details->render(),
-          )).
-      '</div>',
+          )),
       array(
         'title' => 'Diff View',
       ));