Fixed and finished Currency logic

* Finished currency converter ( and tested )
* Added adapters for ExchangeRatesProvider en CurrencyBundle
* Changed and fixed all php class headers for defined
* Cart is only persisted if has lines
* OrderCoupon have more fields. Now saves also, in plain text, Coupon name, code
  and real Amount when was applied
* Applied php-cs-fixer fix
Merge pull request #101 from elcodi/feature/currency-managing

Fixed and finished Currency logic