Edit group configurations.

Ticket: [BLD-1067](https://openedx.atlassian.net/browse/BLD-1067)

**Acceptance criteria:**
* Edit link from Group Configurations page for each group configuration.
* Do not surface group information nor allow groups to be edited (will be a separate story). 

**sandbox:** http://studio.polesye.m.sandbox.edx.org/

@andy-armstrong , @frrrances , @cahrens , @explorerleslie, @mhoeber  please review.
Something that @jzoldak has recommended is that we put a BDD description of what the test is doing in the comments for the test. That way it is easy to understand what the test is covering.

def test_initially_unlocked_visible_to_students(self):
 +        """
For example, 
+        Scenario: An unlocked unit with release date in the past is visible to students
 +            Given I have a published unlocked unit with release date in the past
 +            When I go to the unit page in Studio
 +            Then the unit has a warning that it is visible to students
 +            And it is marked as "RELEASED" with release date in the past visible
 +            And when I click on the View Live Button
 +            And when I view the course as a student
 +            Then I see the content in the unit
 +            """"