Add total amount spent by user

User can see the total amount that he paid for the tickets and total amount spent by him on each ticket

spec/controllers/conference_registration_controller_spec.rb

@@ -252,7 +252,7 @@ describe ConferenceRegistrationsController, type: :controller do
         end
 
         it 'does not assign price of purchased tickets to total_price and purchased tickets to tickets without payment' do
-          expect(assigns(:total_price)).to eq Money.new(0, 'USD')
+          expect(assigns(:total_price)).to eq 0
         end
       end
 
@@ -262,7 +262,7 @@ describe ConferenceRegistrationsController, type: :controller do
         end
 
         it 'assigns 0 dollars to total_price and empty array to tickets variables' do
-          expect(assigns(:total_price)).to eq Money.new(0, 'USD')
+          expect(assigns(:total_price)).to eq 0
           expect(assigns(:tickets)).to match_array []
         end
       end