Implement the GroupContact entity trigger compatibile with all signatures
The post hook (and post insert/update events) have different signatures in CiviCRM core, see dev/core#2585 (closed).
This issue is to identify the different ways CiviCRM core uses the post hook in case of GroupContact. And how each signature looks like and possible fix this in core and in the same way keep CiviRules compatible with the different signatures.
This is related to #101 (closed) and #132 (closed).