FEATURE: Flag count in post menu

This change shows a notification number besides the flag icon in the
post menu if there is reviewable content associated with the post.
Additionally, if there is pending stuff to review, the icon has a red
background.

We have also removed the list of links below a post with the flag
status. A reviewer is meant to click the number beside the flag icon to
view the flags. As a consequence of losing those links, we've removed
the ability to undo or ignore flags below a post.

app/controllers/post_actions_controller.rb

@@ -49,16 +49,6 @@ class PostActionsController < ApplicationController
     end
   end
 
-  def defer_flags
-    guardian.ensure_can_defer_flags!(@post)
-
-    if reviewable = @post.reviewable_flag
-      reviewable.perform(current_user, :ignore)
-    end
-
-    render json: { success: true }
-  end
-
   private
 
   def fetch_post_from_params