PERF: use distributed cache for site text and category slugs

app/models/site_text.rb

@@ -1,18 +1,16 @@
 require_dependency 'site_text_type'
 require_dependency 'site_text_class_methods'
+require_dependency 'distributed_cache'
 
 class SiteText < ActiveRecord::Base
 
-  # needed for site text class methods
-  @mutex = Mutex.new
-  @text_for_cache = {}
   extend SiteTextClassMethods
   self.primary_key = 'text_type'
 
   validates_presence_of :value
 
   after_save do
-    MessageBus.publish '/text_for', self.text_type
+    SiteText.text_for_cache.clear
   end
 
   def self.formats