Ability to change the associated group configuration for a split test

STUD-1658

My sandbox has the latest version of this PR.
http://studio.cahrens.m.sandbox.edx.org/
This is a bit subtle, but the logic only filters out duplicate and edit for blocks that are shown inline.  Those are defined as blocks that have children but that do not have a dedicated URL. For now, this is only inline verticals which we decided we didn't want users to be manipulating.

The only reason that delete is different is that we are allowing delete on inline verticals that represent inactive groups. We decided to always render the delete buttons and then have the CSS control their availability, rather than the template.  Maybe we should have done the same for the other two buttons to keep them consistent.

I double checked, and if I add a content experiment inside another one, then it does correctly get the edit and duplicate buttons.