Allow locale to be set through the front-end

* Store the last used locale in the session
* Allow home page to be identified in helpers even when containing
  parameters
* Create initializer to explicitly set the available locales, the
  default and the load_path

app/helpers/application_helper.rb

@@ -10,10 +10,16 @@ module ApplicationHelper
   end
 
   def home_page?
-    request.fullpath == '/'
+    # Using path because fullpath yields false negatives since it contains
+    # parameters too
+    request.path == '/'
   end
 
   def header_css
     home_page? ? '' : 'results'
   end
+
+  def available_locales_to_switch
+    I18n.available_locales - [I18n.locale]
+  end
 end