Hacked some column sorting onto RatesController

* Added SortHelper to RatesController
* Init and updating the sorting (pre 0.8 sort_update)
* RatesController#index will only render the layout on non-xhr requests
* Changed Rate.history_for_user to take an order clause
* Added rate_sort_header_tag and rate_sort_link to the SortHelper in order
  to get the correct parameters for sorting Rates
* Added rate_sort_header_tags to the Rate lists

  #1915

spec/controllers/rates_controller_spec.rb

@@ -160,10 +160,11 @@ describe RatesController, "as an administrator" do
   describe "responding to GET index with user" do
     before(:each) do
       User.stub!(:find).with(@user.id.to_s).and_return(@user)
+      @default_sort = "#{Rate.table_name}.date_in_effect desc"
     end
 
     it "should expose all historic rates for the user as @rates" do
-      Rate.should_receive(:history_for_user).with(@user).and_return([mock_rate])
+      Rate.should_receive(:history_for_user).with(@user, @default_sort).and_return([mock_rate])
       get :index, :user_id => @user.id
       assigns[:rates].should == [mock_rate]
     end
@@ -172,7 +173,7 @@ describe RatesController, "as an administrator" do
   
       it "should render all rates as xml" do
         request.env["HTTP_ACCEPT"] = "application/xml"
-        Rate.should_receive(:history_for_user).with(@user).and_return(rates = mock("Array of Rates"))
+        Rate.should_receive(:history_for_user).with(@user, @default_sort).and_return(rates = mock("Array of Rates"))
         rates.should_receive(:to_xml).and_return("generated XML")
         get :index, :user_id => @user.id
         response.body.should == "generated XML"