controllers: refactor rate limits.

Refactor controllers so that endpoint rate limits are declared locally,
with the endpoint, instead of globally, in a single method in ApplicationController.

This way an endpoint's rate limit is declared in the same file as the
endpoint itself.

This is so we can add fine-grained rate limits for certain GET requests.
Before rate limits were only for non-GET requests.

app/controllers/favorites_controller.rb

@@ -1,6 +1,9 @@
 class FavoritesController < ApplicationController
   respond_to :js, :json, :html, :xml
 
+  rate_limit :create,  rate: 1.0/1.second, burst: 200
+  rate_limit :destroy, rate: 1.0/1.second, burst: 200
+
   def index
     post_id = params[:post_id] || params[:search][:post_id]
     user_id = params[:user_id] || params[:search][:user_id]