WIP : CFD-148 create group dashboard

- Created extra ctools plugins to detect the group context.
- Created the group dashboard page.
Reworked to:
  @api
  Scenario: Check dashboard content as group owner
    Given I am logged in as user "mariecurie"
    When I visit the dashboard of group "Movie Popcorn Corner"
    Then I should see the group dashboard

The "I should see the group dashboard" holds the meta steps:
* I should have access to the page
* Group menu item "Home" should be active
* I should see the Quick Post form
* I should see the Activity stream