FEATURE: support for emoji sets

Added following emoji sets
  - Apple/International
  - Emoji One (default)
  - Android/Google
  - Twitter

FIX: translations from plugins weren't properly merged with default translations
FEATURE: new 'site_setting_changed' event

db/migrate/20141211114517_fix_emoji_path.rb

@@ -0,0 +1,19 @@
+class FixEmojiPath < ActiveRecord::Migration
+  BASE_URL = '/plugins/emoji/images/'
+
+  def up
+    execute <<-SQL
+      UPDATE posts
+         SET cooked = REPLACE(cooked, '#{BASE_URL}', '#{BASE_URL}emoji_one/')
+       WHERE cooked LIKE '%#{BASE_URL}%'
+    SQL
+  end
+
+  def down
+    execute <<-SQL
+      UPDATE posts
+         SET cooked = REPLACE(cooked, '#{BASE_URL}emoji_one/', '#{BASE_URL}')
+       WHERE cooked LIKE '%#{BASE_URL}emoji_one/%'
+    SQL
+  end
+end