create new base class for child objects #161
Description
Instead of, or in addition to, having a field on child objects with the RelativityObjectFieldParentArtifactId attribute, we may just want to create a ChildBaseDto : BaseDto that has a ParentArtifactId.
To get the name of the field for querying, we could either make the ParentArtifactId property abstract and force people to use an attribute, or query for the parent field and just cache it.
This might be easier after #158 .