modifyTime and modifierUuid for groups and stems when memberships get updated

Currently when you add or delete a member or privilege from a group or stem, the modifyTime and modifierUuid for the group or stem is also updated. We would like to stop this from happening and instead create last_membership_change attributes on groups and stems that get updated upon membership changes. The update to last_membership_change would be optional and controlled in the properties file. The group or stem's modifyTime and modifierUuid would still get updated when the object is modified in other ways, such as an attribute change. One of the motives behind this change is to improve performance.

We also need to create the following query filters:

GroupMembershipModifiedAfterFilter.java
GroupMembershipModifiedBeforeFilter.java

Also, if this affects LDAPPC, changes may be required there also.