Add the time specification to the invoice_form view; update it

Generation of a time specification appendix can be enabled for each invoice
indepently on whether it is or is not enabled for the customer.  However,
whether it is enabled by default when an invoice is created, that does
follow the setting for the customer.

stoptime.rb

@@ -1056,6 +1056,7 @@ module StopTime::Controllers
       invoice = Invoice.create(:number => number)
       invoice.customer = Customer.find(customer_id)
       invoice.company_info = CompanyInfo.last
+      invoice.include_specification = invoice.customer.time_specification
 
       # Handle the hourly rated tasks first by looking at the selected time
       # entries.
@@ -1143,6 +1144,7 @@ module StopTime::Controllers
     def post(customer_id, invoice_number)
       invoice = Invoice.find_by_number(invoice_number)
       invoice.paid = @input.has_key? "paid"
+      invoice.include_specification = @input.has_key? "include_specification"
       invoice.save
 
       redirect R(CustomersNInvoicesX, customer_id, invoice_number)
@@ -2040,6 +2042,12 @@ module StopTime::Views
               _form_input_checkbox("paid")
             end
           end
+          div.control_group do
+            label.control_label "Include specification?"
+            div.controls do
+              _form_input_checkbox("include_specification")
+            end
+          end
           div.form_actions do
             button.btn.btn_primary "Update", :type => :submit,
               :name => "update", :value => "Update"