Provide "diff-1up" and "diff-2up" classes and tweak some styles

Summary: Ref T2009. Remove forced min-width of 780px in 1-up mode, and tweak a few other things to look better.

Test Plan: Looks better on mobile.

Reviewers: btrahan, chad

Reviewed By: chad

Subscribers: epriestley

Maniphest Tasks: T2009

Differential Revision: https://secure.phabricator.com/D11974

resources/celerity/map.php

@@ -10,7 +10,7 @@ return array(
     'core.pkg.css' => '1a530a25',
     'core.pkg.js' => 'a77025a1',
     'darkconsole.pkg.js' => '8ab24e01',
-    'differential.pkg.css' => '4c3242f8',
+    'differential.pkg.css' => 'd8866ed8',
     'differential.pkg.js' => '7b5a4aa4',
     'diffusion.pkg.css' => '591664fa',
     'diffusion.pkg.js' => 'bfc0737b',
@@ -55,7 +55,7 @@ return array(
     'rsrc/css/application/dashboard/dashboard.css' => '17937d22',
     'rsrc/css/application/diff/inline-comment-summary.css' => 'eb5f8e8c',
     'rsrc/css/application/differential/add-comment.css' => 'c478bcaa',
-    'rsrc/css/application/differential/changeset-view.css' => 'a7781046',
+    'rsrc/css/application/differential/changeset-view.css' => 'b600950c',
     'rsrc/css/application/differential/core.css' => '7ac3cabc',
     'rsrc/css/application/differential/results-table.css' => '181aa9d9',
     'rsrc/css/application/differential/revision-comment.css' => '48186045',
@@ -519,7 +519,7 @@ return array(
     'conpherence-notification-css' => '04a6e10a',
     'conpherence-update-css' => '1099a660',
     'conpherence-widget-pane-css' => '3d575438',
-    'differential-changeset-view-css' => 'a7781046',
+    'differential-changeset-view-css' => 'b600950c',
     'differential-core-view-css' => '7ac3cabc',
     'differential-inline-comment-editor' => 'f2441746',
     'differential-results-table-css' => '181aa9d9',