Fixed and finished Currency logic

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature? | yes
| BC Breaks? | yes
| Deprecations?     | yes
| Tests pass?    | yes
| Fixed tickets | -
| LICENSE | MIT

* 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