add payment mode field to tickets for attendees

app/views/tickets/index.html.haml

@@ -14,6 +14,7 @@
           %thead
             %tr
               %th Ticket
+              %th Payment
               %th Quantity
               %th Price
               %th Total
@@ -21,6 +22,7 @@
           - @conference.tickets.each do |ticket|
             = render partial: 'ticket', f: f, locals: {ticket: ticket}
           %tr
+            %td
             %td
             %td
             %td.col-sm-1.col-md-1.text-center
@@ -43,4 +45,4 @@
     .col-md-13
       %p.text-muted.text-center
         %small
-          * Buying a ticket is not mandatory. Checkout will be at the conference registration.
+          * Buying a ticket is not mandatory. Checkout will be at the conference registration.