Behat 3 support

• support Behat 3 and Symfony 3
• bug fixes
• add url verification in open() and isOpen()
• allow to override page parameters
• allow injecting page objects directly to context's constructor
• enable custom factories and factory configuration
• enable multiple namespace configuration
• avoid calls to mink deprecated methods
• enable proxy dir configuration for lazy factory (used when injecting page objects into a context constructor)