Remove page file dir from frontend. Resolves #1052 #1241 (#1369)

* Remove all references to page_file_dir. Use new method signature for Wiki#page. Refactor helpers.
* Use write_file for uploads
* Refactor /pages route

lib/gollum/views/layout.rb

@@ -24,16 +24,12 @@ module Precious
         !@path.nil?
       end
 
-      def page_dir
-        @page_dir
-      end
-
       def base_url
         @base_url
       end
 
       def custom_path
-        "#{@base_url}#{@page_dir.empty? ? '' : '/'}#{@page_dir}"
+        "#{@base_url}"
       end
 
       def css # custom css