Add price_formatted and list_price_formatted fields

[pikulsky]

Clerk module has built-in "price" and "list_price" fields to sync. They both are float.
When it comes to display these prices to user, for the moment it's possible to use Clerk's formatting methods (see https://docs.clerk.io/docs/template-language), there are two functions: "money" and "money_eu". E.g.:
{{money price 2 "," "."}}
{{money list_price 2 "," "."}}

This way the information how to format a currency is doubled: Magento itself has currency format for prices, now Clerk should know how to format prices. I think the better approach is to have a "single source of truth": so, Magento formats prices and sends it to Clerk, Clerk should not keep any logic how to format data, Clerk should display it as it is.