Integrate with Group module

This code doesn't work for me, as it doesn't work where roles are sync'd or inherited from global roles, only when group roles are manually assigned.

BTW I've updated this code to be compatible with 3.x of workbench_email and 3.x of Group module. I pushed this code to a different branch 3302006-integrate-with-group-3x in the issue fork for the record.

I've updated the 3x version with this code that works for synced roles

This issue 💬 Group::getMembers() returns empty for syncronized roles Fixed is where Webform Group module discussed the problem, but there wasn't any indication that this is a Group module bug or feature gap.

Just adding a physical patch as well for my client's clarity.