Updated the code for the refactorings of the context in Behat
Bumped the composer constraint to prevent installing RC1

This extension relies on all non-BC changes done after the RC1 release.
Changed the suite type from symfony-bundle to symfony_bundle
Refactored the way symfony bundle suites are generated

A SymfonyBundleSuite instance is created now, allowing to identify such
suites in other parts of Behat.
Reimplemented the support of bundle feature locators

The changes done in Gherkin 4.0 make it possible.