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/views/stream_entries/embed.html.haml

@@ -1,2 +1,3 @@
-.activity-stream.activity-stream-headless
-  = render @type, @type.to_sym => @stream_entry.activity, centered: true
+- cache @stream_entry.activity do
+  .activity-stream.activity-stream-headless
+    = render "stream_entries/#{@type}", @type.to_sym => @stream_entry.activity, centered: true