Initial assortment features

* Add drafts of option, property and prototype features.
* Update vendors.
Add basic product scenarios
Add step definitions and adjust features
Tweak the assortment features and configuration

* Update vendors.
* Adjust the assortment bundle features.
* Tweak the Behat configuration.
* Add StofDoctrineExtensionsBundle.
Add product variants scenarios, use lower case btn labels
Update SyliusWebBundle
Add variant generation and prototype building features
Merge pull request #10 from Sylius/assortment-bundle-integration

Initial assortment features