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

Martin Lowe requested to merge malowe/git-eca-rest-api:malowe/master/66 into master

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.

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