Update status embeds (#4742)

- Use statuses controller for embeds instead of stream entries controller
- Prefer /@:username/:id/embed URL for embeds
- Use /@:username as author_url in OEmbed
- Add follow link to embeds which opens web intent in new window
- Use redis cache in development
- Cache entire embed

app/controllers/stream_entries_controller.rb

@@ -25,10 +25,7 @@ class StreamEntriesController < ApplicationController
   end
 
   def embed
-    response.headers['X-Frame-Options'] = 'ALLOWALL'
-    return gone if @stream_entry.activity.nil?
-
-    render layout: 'embedded'
+    redirect_to embed_short_account_status_url(@account, @stream_entry.activity), status: 301
   end
 
   private