We should add basic doc to BehatBundle.

For 7.x and master: README describing how to use BehatBundle features

• Behat extension (how to inject services into Contexts)
• available Contexts
• how to login into repository
• how to use
• running Behat Selenium tests (use https://ezno.sharepoint.com/:w:/r/sites/QA/_layouts/15/Doc.aspx?sourcedoc=%7B6358799F-B457-45BB-83E6-D0384350BB15%7D&file=RunningTestBehatV2.docx&action=default&mobileredirect=true )

For 7.x: mark all deprecated classes as such

For master: list of features dropped from 7.x and how to upgrade