Behat 3 upgrade

Upgrade to Behat 3

Changes:
- [x] Minor update on sentences
- [X] Update DemoContext to reflect changes of Behat Upgrade
- [x] Update ContentContext to reflect changes of Behat Upgrade

To do:
- [x] pass on that PR (https://github.com/ezsystems/ezpublish-community/pull/182)
Actually all tests depend on SetupWizard but not the other way around
Demo was previously running without testing REST, and it should keep it that way (imho).
REST is only being tested on BehatBundle and Community at the moment, but we should make those run also on Kernel

@joaoinacio this was wrong copy paste. thanks