🎨 rename redirects middleware to custom-redirects

no issue

- we had two middlewares:
  1. url-redirects
  2. redirects

- this was confusing, so i renamed (2) to custom redirects

custom-redirects.js: you can define custom redirects for your blog in a JSON file
url-redirects.js: Ghost takes care of required admin url or SSL redirects

core/server/blog/app.js

@@ -21,7 +21,7 @@ var debug = require('debug')('ghost:blog'),
     serveSharedFile = require('../middleware/serve-shared-file'),
     staticTheme = require('../middleware/static-theme'),
     themeHandler = require('../middleware/theme-handler'),
-    customRedirects = require('../middleware/redirects'),
+    customRedirects = require('../middleware/custom-redirects'),
     serveFavicon = require('../middleware/serve-favicon');
 
 module.exports = function setupBlogApp() {