Add fields to attr_reader.
Add reader for best_selling_count and latest_dates.
Add tests for all fields in attr_reader list.
Refactor the admin/statistics/sales_orders.
Move all logic to the presenter class.
Adjust the view.
Change all to each because of using database_cleaner.
Add top_customer to sales_order_item model.
Refactor Customer.top_by_sum_total_price.
Import PostgresStatisticable and FormatterHelper lib.
Implement tests.
Add sums_of_tops to customer model.
Remove destroy_all because of database_cleaner.
Refactor admin/statistics/customers.
Move logic to customers_presenter.
Update tests.
Set .sass-cache as a ignoring file.
Add sum_ext_price_by_sales_agent_and_category to sales_order_item model.
Refactor admin/statistics/sales_agents.
Move some code to presenter.
Implement tests.
Refactor admin/statistics/sales_regions.
Move codes to presenter.
Implement tests.