Add support for meta tags in locales

Fixed kpumuk#83 creating support for adding meta tags via locales in the
format:
en:
  meta_tags:
    `controller`:
      `action`:
        title: My title
etc.

I have not created any tests as I’m quite frankly not sure how to write
them using locales data.

README.md

@@ -323,6 +323,21 @@ Also you could use `set_meta_tags` method to define all meta tags simultaneously
 
 You can find allowed options for `set_meta_tags` method below.
 
+### Using MetaTags in locales with I18n
+
+You can define title, description and keywords of any view in your locales file.
+    en:
+      meta_tags:
+        visitors:
+          index:
+            title: My page title
+            description: My page description
+            keywords: My, Page, Keywords
+
+This would default the controller `visitors` with action `index` title, description and keywords.
+You can still overwrite them from a view or controller like normally.
+
+
 ### Using MetaTags in view
 
 To set meta tags you can use following methods:

lib/meta_tags/controller_helper.rb

@@ -14,6 +14,7 @@ module ControllerHelper
 
     included do
       alias_method_chain :render, :meta_tags
+      before_filter: :meta_tags_from_locales
     end
 
     # Processes the <tt>@page_title</tt>, <tt>@page_keywords</tt>, and
@@ -27,6 +28,19 @@ def render_with_meta_tags(*args, &block)
     end
     protected :render_with_meta_tags
 
+    # Processes meta tags from locales file in the name space
+    # [locale].meta_tags.[controller_name].[action].[title|description|keywords]
+    # So en.meta_tags.visitors.index.title would be loaded as title for default
+    # welcome page in the visitors controller in english.
+    def meta_tags_from_locales
+      name_space = "meta_tags.#{controller_name}.#{action_name}"
+
+      self.meta_tags[:title]       = I18n.t("#{name_space}.title") unless I18n.t("#{name_space}.title", default: '').blank?
+      self.meta_tags[:keywords]    = I18n.t("#{name_space}.keywords") unless I18n.t("#{name_space}.keywords", default: '').blank?
+      self.meta_tags[:description] = I18n.t("#{name_space}.description") unless I18n.t("#{name_space}.description", default: '').blank?
+    end
+    protected :meta_tags_from_locales
+
     # Set meta tags for the page.
     #
     # See <tt>MetaTags::ViewHelper#set_meta_tags</tt> for details.