Ability to change the associated group configuration for a split test

STUD-1658

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http://studio.cahrens.m.sandbox.edx.org/
Good catch on the i18n. I think it is the notifier's job to specify a localized message, so I'll just fix the hard-coded string. I'd like to get ORA to pass through their own title so that I can remove this ugly default title, but I can't do that in one step.