Added support for product variants

See https://github.com/elcodi/elcodi/pull/146 for details about Product
Variants

Commits with following titles were squashed:
* Controllers
* CartController now supports product variant
* Small twig improvements
* Flashbag notification at login failure
* Added AJAX interaction when choosing variants
* Fixed product view parameters
* Updated required packages version
* Small code style fixes
* Removed add-basket-box from variant view
* Title in home page view
Merge pull request #13 from elcodi/variant-product

Variant product frontend implementation