Improved product view

Improved product view
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

Removed assignement of provider into views and fixed error from previous
merge