Pull cc.xml URL generation into a helper.

Makes it easier to overwrite in pro-web for tokenized URLs.

assets/scripts/app/helpers/status_image_formatter.coffee

@@ -51,5 +51,5 @@
   )
 
   ccxmlStatusUrl: (->
-    "#{Travis.config.api_endpoint}/repos/#{@slug}/cc.xml"
+    Travis.Urls.ccXml(@slug)
   )

assets/scripts/app/helpers/urls.coffee

@@ -23,6 +23,9 @@
   statusImage: (slug, branch) ->
     "#{location.protocol}//#{location.host}/#{slug}.svg" + if branch then "?branch=#{branch}" else ''
 
+  ccXml: (slug) ->
+    "#{Travis.config.api_endpoint}/repos/#{slug}/cc.xml"
+
   email: (email) ->
     "mailto:#{email}"