Create new group configurations page.

**Ticket**: [BLD-1121](https://edx-wiki.atlassian.net/browse/BLD-1121)

**Acceptance criteria:**
* Button (or something) on the Group Configurations page to create a new configuration. 
* Editable fields appear for: 
  * Group Configuration Name (required, ok if non-unique)
  * Group Configuration ID (READ-ONLY, required, numeric, must be unique within a course - can just increment sequentially for courses with no existing but take into account courses with existing group configurations created in the user_partitions value on Advanced Settings page - we must not overwrite any values.)
  * Group Configuration Description (optional)
* DO NOT show any Groups information on the front end (will be a separate story) but DO create default groups (2 groups, named Group A & Group B, both at 50% allocation) on the backend. (This should already be handled by the split_test module, but we should test to make sure this reflects correctly in the Group Configurations page.)
* Create button should save the group configuration.
  * Error message should appear if required fields are omitted upon save. 
  * User should stay in the New/Edit Experiment modal to correct the error. 
* Cancel link should not save but should close the new group configuration modal. 

**sandbox:** http://studio.olmar.m.sandbox.edx.org/

@andy-armstrong , @cahrens , @frrrances please review.
@polesye It is a very interesting question as to when to do Jasmine tests versus Bok Choy tests. We haven't fully settled on the best approach here, and you are right that we might be double testing. 

My preference is to do thorough testing in Jasmine so that we get full coverage and so that we are confident in the JavaScript. In particular, it isn't possible to fake bad server responses in Bok Choy and see how the UI handles those cases. If we decide to leave more testing to Bok Choy then we will have to accept less than 100% coverage on JavaScript which seems contrary to our goal of increasing our coverage.

However, that's just my opinion. @cahrens @jzoldak anything to add?