Iss. #66 - Add support for new Gitlab nesting strategy

As we move to the nested group model in Gitlab, we need the ECA to support it as well. This is a full switch over, so I removed the old code since it won't be needed. I've updated the tests as well, adding in a test for the ignored groups as well.

requested review from @cguindon, @heurtemattes, and @mbarbero

approved this merge request

merged

mentioned in commit 5c317d45