Refactor and improve invoices

- `runner 'Invoice.cancel_overdue_invoices'` in `schedule.rb` is
changed to `rake 'invoices:cancel_overdue'`.
- `invoices.payment_term` database column is removed and its value is
hardcoded in UI.
- `invoices.paid_at` is removed as unused
- `invoices.due_date` column's type is now `date`.
- `Invoice#invoice_items` renamed to `Invoice#items` and `Invoice`
interface to get a list of items is unified.
- Default date format in UI.
- Default translations are used.
- Tests improved.
- Specs converted to tests and removed along with factories.
- Database structure improved.

config/initializers/initial_settings.rb

@@ -40,7 +40,6 @@ if con.present? && con.table_exists?('settings')
   Setting.save_default(:directo_monthly_number_max,  309999)
   Setting.save_default(:directo_monthly_number_last, 309901)
   Setting.save_default(:days_to_keep_invoices_active, 30)
-  Setting.save_default(:days_to_keep_overdue_invoices_active, 30)
   Setting.save_default(:minimum_deposit, 0.0)
   Setting.save_default(:directo_receipt_payment_term, "R")
   Setting.save_default(:directo_receipt_product_name, "ETTEM06")

config/locales/account_activities.en.yml

@@ -0,0 +1,5 @@
+en:
+  activerecord:
+    attributes:
+      account_activity:
+        created_at: Receipt date

config/locales/admin/invoices.en.yml

@@ -0,0 +1,5 @@
+en:
+  admin:
+    invoices:
+      cancel:
+        cancelled: Invoice has been cancelled

config/locales/en.yml

@@ -523,12 +523,10 @@ en:
   domain_not_found: 'Domain was not found'
   new_contact: 'New contact'
   add_deposit: 'Add deposit'
-  amount: 'Amount'
   please_pay_the_following_invoice: 'Please pay the following invoice'
   invoice_no: 'Invoice no. %{no}'
   invoice_number: Invoice no.
   seller: 'Seller'
-  prepayment: 'Prepayment'
   unpaid: 'Unpaid'
   your_current_account_balance_is: 'Your current account balance is %{balance} %{currency}'
   billing: 'Billing'
@@ -588,7 +586,6 @@ en:
     refers to the computer that saves and forwards notices related to the Domain Names and their corresponding IP addresses in the Internet.
   account_activity: 'Account activity'
   account_activities: 'Account activities'
-  receipt_date: 'Receipt date'
   manual_binding: 'Manual binding'
   transaction_is_already_binded: 'Transaction is already binded'
   invoice_was_not_found: 'Invoice was not found'
@@ -614,9 +611,6 @@ en:
   certificates: 'Certificates'
   cancel: 'Cancel'
   cancelled: 'Cancelled'
-  cancel_date: 'Cancel date'
-  cannot_cancel_paid_invoice: 'Cannot cancel paid invoice'
-  cannot_cancel_cancelled_invoice: 'Cannot cancel cancelled invoice'
   cannot_bind_cancelled_invoice: 'Cannot bind cancelled invoice'
   minimum_invoice_no: 'Miminum invoice no'
   maximum_invoice_no: 'Maximum invoice no'

config/locales/registrar/invoices.en.yml

@@ -9,3 +9,6 @@ en:
       payment_complete: Credit Card payment Complete
       index:
         reset_btn: Reset
+
+      cancel:
+        cancelled: Invoice has been cancelled

config/schedule.rb

@@ -22,7 +22,7 @@ if @cron_group == 'registry'
   end
 
   every :day, at: '12:10am' do
-    runner 'Invoice.cancel_overdue_invoices'
+    rake 'invoices:cancel_overdue'
   end
 
   # TODO