Add ability to set a header image per Phame blog

Summary: This is the backend half of uploading an image as a header for Phame Blogs. Allows you to upload image, or delete it. Ref T10901

Test Plan:
Go to Manage Blog, visit Edit Header Image, Upload snarky file. See snarky file on Manage page. Edit Header Image, click delete, save, see file goes away.

{F1690966}

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T10901

Differential Revision: https://secure.phabricator.com/D16140

resources/celerity/map.php

@@ -7,7 +7,7 @@
  */
 return array(
   'names' => array(
-    'core.pkg.css' => '6913fe66',
+    'core.pkg.css' => 'c7fc5aec',
     'core.pkg.js' => '10275c16',
     'darkconsole.pkg.js' => 'e7393ebb',
     'differential.pkg.css' => 'b3eea3f5',
@@ -155,7 +155,7 @@ return array(
     'rsrc/css/phui/phui-spacing.css' => '042804d6',
     'rsrc/css/phui/phui-status.css' => 'd5263e49',
     'rsrc/css/phui/phui-tag-view.css' => '6bbd83e2',
-    'rsrc/css/phui/phui-timeline-view.css' => '6e342216',
+    'rsrc/css/phui/phui-timeline-view.css' => '8ea41b25',
     'rsrc/css/phui/phui-two-column-view.css' => '9fb86c85',
     'rsrc/css/phui/workboards/phui-workboard-color.css' => 'ac6fe6a7',
     'rsrc/css/phui/workboards/phui-workboard.css' => 'e6d89647',
@@ -860,7 +860,7 @@ return array(
     'phui-status-list-view-css' => 'd5263e49',
     'phui-tag-view-css' => '6bbd83e2',
     'phui-theme-css' => '027ba77e',
-    'phui-timeline-view-css' => '6e342216',
+    'phui-timeline-view-css' => '8ea41b25',
     'phui-two-column-view-css' => '9fb86c85',
     'phui-workboard-color-css' => 'ac6fe6a7',
     'phui-workboard-view-css' => 'e6d89647',