Adding a shellAccess tag to features requiring this, and a preliminary BeforeScenario hook to test for access.

Moving drush alias config, and base_url config to behat.local.yml, adding behat.local.yml.example file.

Adding an override of MinkContext::locatePath() to get around the fact that Selenium doesn't support basic auth.

Replacing the internal code of some of our step definitions with existing code from the Mink extensions.

Added MinkContext to take advantage of the step library; altered existing steps to remove ambiguity.