FusionDirectory to mimic memberOf feature in a new plugin

Descriptive title for this enhancement

There are cases where the memberOf attribute is still useful but the overlay can suffer from performance for very big groups.

FusionDirectory already have many kind of references between users and groups. The idea would be to mimic the overlay comportment in FusionDirectory. It will minimize the impact on big groups because we are already dealing with references.

Actual behavior

Plugin doesn't exist

Expected behavior

Making a new plugin

Step by step description of new behaviour

1. Installing the new plugin
2. Make options if needed for fusiondirectory configuration
3. Any modification in a group will add the memberOf attribute in the user

Benefits

Advantage of memberOf overlay without the downside for bigger groups

Possible Drawbacks

None