Remove exchange rate API

Exchange rate API should be removed from code base.
It introduces unnecessary complexity into the system and prevents natural flow of product information in the system.
I.e. to enable price list in a different currency all is needed is to create spreadsheet in XLS use exchange rate formula and then import into the system. Moreover during this process marketologist is able to clean up "ugly" prices. E.g. if the exchange rate gives prices like 197.36 - looks quite eye catching, rather than 197.00. So it is up to marketologist to craft alternative prices. By doing so all natural tools like start/end date for price lists, filtered navigation, indexing, etc become available with ease.