Use new product helper

Add sonata_product_cheapest_variation_price new product helper method + phpdoc fix
Fixed failing currency test
Merge pull request #29 from Bladrak/fixCurrencyTest

Fixed failing currency test
Merge pull request #28 from eko/develop

SONATA-293 - Fix cheapest product variations price display on cross-sell...
Minor fixes on product page and added unit tests

SONATA-294 - Changed product page variations display
Added default form behavior

Added redirection if a product have a single enabled variation

Fixed case when a root product has no enabled variation

SONATA-294 - Minor fix and added unit tests
Merge related to PR #22
Changes made related to PR #26 feedbacks