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.

app/controllers/admin/invoices_controller.rb

@@ -33,13 +33,8 @@ module Admin
     end
 
     def cancel
-      if @invoice.cancel
-        flash[:notice] = t(:record_updated)
-        redirect_to([:admin, @invoice])
-      else
-        flash.now[:alert] = t(:failed_to_update_record)
-        render :show
-      end
+      @invoice.cancel
+      redirect_to [:admin, @invoice], notice: t('.cancelled')
     end
 
     def forward

app/controllers/registrar/invoices_controller.rb

@@ -6,8 +6,7 @@ class Registrar
 
     def index
       params[:q] ||= {}
-      invoices = current_registrar_user.registrar.invoices
-                   .includes(:invoice_items, :account_activity)
+      invoices = current_registrar_user.registrar.invoices.includes(:items, :account_activity)
 
       normalize_search_parameters do
         @q = invoices.search(params[:q])
@@ -35,13 +34,8 @@ class Registrar
     end
 
     def cancel
-      if @invoice.cancel
-        flash[:notice] = t(:record_updated)
-        redirect_to([:registrar, @invoice])
-      else
-        flash.now[:alert] = t(:failed_to_update_record)
-        render :show
-      end
+      @invoice.cancel
+      redirect_to [:registrar, @invoice], notice: t('.cancelled')
     end
 
     def download_pdf
@@ -58,18 +52,7 @@ class Registrar
     def normalize_search_parameters
       params[:q][:total_gteq].gsub!(',', '.') if params[:q][:total_gteq]
       params[:q][:total_lteq].gsub!(',', '.') if params[:q][:total_lteq]
-
-      ca_cache = params[:q][:due_date_lteq]
-      begin
-        end_time = params[:q][:due_date_lteq].try(:to_date)
-        params[:q][:due_date_lteq] = end_time.try(:end_of_day)
-      rescue
-        logger.warn('Invalid date')
-      end
-
       yield
-
-      params[:q][:due_date_lteq] = ca_cache
     end
   end
 end

app/controllers/registrar/payments_controller.rb

@@ -29,7 +29,7 @@ class Registrar
       if @payment.valid_response_from_intermediary? && @payment.settled_payment?
         @payment.complete_transaction
 
-        if invoice.binded?
+        if invoice.paid?
           flash[:notice] = t(:pending_applied)
         else
           flash[:alert] = t(:something_wrong)