Cucumber test refactoring and new feature for creating a course as an administrator

Refactoring:
    Logging in as admin step definition: moved from create_team_assignment_add_participants to authentication_steps
    Clicking on links: changed regex selector to allow multiple word
    strings
Extracted duplicated steps into Background blocks
Extracted duplicated steps into a Background block
Extracted duplicated steps into a Background block
added a step definition to create a table of users