Adding acceptance tests for a dialog box

The Git tag for this section is new-sharing-scenarios.

Let's start by taking a look at the new feature:

1. Open the features/sharing.feature file and take a look at the first feature that you've been given. Read through the steps and try to understand what our product owner is describing. The test covers quite a lot of behavior – unlike our unit tests. That is to say, it tells a complete story, or use case:

Scenario: Presenter chooses to reset current state when sharing
  Given the presenter navigated to the application page
  And the presenter entered the following instructions at the prompt:
    | forward 10 |
    | right 90 |
  And the presenter clicked the button 'startSharing'
  When the presenter clicks the button 'reset'
  And the observer navigates to the presenter's sharing link
  Then the observer...